To reproduce: run the sample project and scroll to the end of the view. You will notice that the tasks are not properly aligned. You can increase the GraphicalViewElement.OnePixelTime in order to make the alignment even worse.

Workaround: Adjust the GraphicalViewElement.OnePixelTime in order to obtain the correct alignment.

How to reproduce: 
  this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineRange = Telerik.WinControls.UI.TimeRange.DayQuarterHours;
  this.radGanttView1.GanttViewElement.GraphicalViewElement.AutomaticTimelineTimeRange = true;
  this.radGanttView1.GanttViewElement.GraphicalViewElement.OnePixelTime = new TimeSpan(0, 0, 15);

Workaround: at the moment the Gantt control does not support an automatic timeline range for day quarter hours. The TimeRange.DayQuarterHours is similar to the half days and they should be handled the same way when in automatic timeline. If possible TimeRange.DayHalfHours 
this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineRange = Telerik.WinControls.UI.TimeRange.DayHalfHours;

To reproduce: click (mouse down) on a task but then release the mouse button off the task. It then stays selected even when I click on other tasks. You can repeat this over and over and end up with every task as "selected" as shown in the video.

Workaround:

 AddHandler Me.RadGanttView1.GraphicalViewItemFormatting, AddressOf GraphicalViewItemFormatting

Private Sub GraphicalViewItemFormatting(sender As Object, e As GanttViewGraphicalViewItemFormattingEventArgs)
    Dim taskItem As GanttViewTaskItemElement = TryCast(e.ItemElement, GanttViewTaskItemElement)
    If taskItem IsNot Nothing AndAlso taskItem.TaskElement.VisualState.Contains(".MouseDown") AndAlso Not taskItem.Selected Then
        taskItem.TaskElement.IsMouseDown = False
    End If
End Sub

To reproduce:

public Form1()
{
    InitializeComponent();

    DataTable tasks = new DataTable("Tasks");
    tasks.Columns.Add("Id", typeof(int));
    tasks.Columns.Add("ParentId", typeof(int));
    tasks.Columns.Add("Title", typeof(string));
    tasks.Columns.Add("Start", typeof(DateTime));
    tasks.Columns.Add("End", typeof(DateTime));
    tasks.Columns.Add("Progress", typeof(decimal));
    DataTable links = new DataTable("Links");
    links.Columns.Add("StartId", typeof(int));
    links.Columns.Add("EndId", typeof(int));
    links.Columns.Add("LinkType", typeof(int));
    DataSet data = new DataSet();
    data.Tables.Add(tasks);
    data.Tables.Add(links);

    Random rand = new Random();
    int cnt = 3000;
    int cnt2 = 6000;
    for (int i = 1; i < cnt; i++)
    {
        tasks.Rows.Add(i, 0, "Summary task title", DateTime.Now.AddDays(i), DateTime.Now.AddDays(i + 5), 30m);
    }

    for (int i = cnt; i < cnt2; i++)
    {
        tasks.Rows.Add(i, rand.Next(1, cnt), "First child task title", new DateTime(2010, 10, 10), new DateTime(2010, 10, 12), 10);  
    }
    for (int i = 0; i < 2000; i++)
    {
        links.Rows.Add(rand.Next(cnt, cnt2), rand.Next(1, cnt), 1);
    } 
    
    
    this.radGanttView1.GanttViewElement.TaskDataMember = "Tasks";
    this.radGanttView1.GanttViewElement.ChildMember = "Id";
    this.radGanttView1.GanttViewElement.ParentMember = "ParentId";
    this.radGanttView1.GanttViewElement.TitleMember = "Title";
    this.radGanttView1.GanttViewElement.StartMember = "Start"; 
    this.radGanttView1.GanttViewElement.EndMember = "End";
    this.radGanttView1.GanttViewElement.ProgressMember = "Progress";
    this.radGanttView1.GanttViewElement.LinkDataMember = "Links";
    this.radGanttView1.GanttViewElement.LinkStartMember = "StartId";
    this.radGanttView1.GanttViewElement.LinkEndMember = "EndId";
    this.radGanttView1.GanttViewElement.LinkTypeMember = "LinkType";
    this.radGanttView1.GanttViewElement.DataSource = data;
    this.radGanttView1.Columns.Add("Start");
    this.radGanttView1.Columns.Add("End");
}

private void radButton1_Click(object sender, EventArgs e)
{
    this.radGanttView1.PrintPreview();
}

How to reproduce:

1. Run the project 
2. Press the radButton1 
3. Edit description of the first line (Line whose Identifier is TestProject1) 
4. Clicking some other line to end the edit causes the ASSERT to come up 

To reproduce: please refer to the attached sample project. Try to edit the title for one of the child tasks in the grid and click the 

Workaround:

private void radGanttView1_ItemChanged(object sender, Telerik.WinControls.UI.GanttViewItemChangedEventArgs e)
{
    IEditableObject editebleObejct = e.Item.DataBoundItem as IEditableObject;
    if (editebleObejct != null)
    {
         editebleObejct.EndEdit();
    }
}

To reproduce:
1) Open the Demo application >> Settings example.
2) Select a task and activate the editor for it.
3) Delete the task by clicking the button above.

It may be necessary to repeat the steps several times. The error is not reproduced immediately. 

To reproduce:
- Set the range to lest than one day.
- Set the TimelineRange to DayHalfHours

Workaround: 
Make sure that the range is at least one day. 

Hey,

We have a problem with the GanttViewTimeLineContainer as you see in the screeshot  : gantt_print2.png

When we are in TimeLineRange = TimeRange.Year and we print the gantt, we have a problem with the appearence of GanttViewTimeLineContainer, we can see the first line with the year (it's ok) but after, the second line we can see a reperition of all month : jfmamjjasond jfmamjjasond jfmamjjasond jfmamjjasond etc etc etc

Can we change the appearence ? Do you have an explanation for this visualization ? 

Thank you,

Regards,

Valériane E.

Please look at the attached screenshot.

Workaround: you can replace the StackLayoutElement used in the GanttViewTimelineItemBottomStackElement with a DockLayoutPanel for example as follows:

Public Class CustomGanttViewTimelineItemElement
Inherits GanttViewTimelineItemElement
    Public Sub New(data As GanttViewTimelineDataItem, graphicalViewElement As GanttViewGraphicalViewElement)
        MyBase.New(data, graphicalViewElement)

    End Sub
    Dim dock As DockLayoutPanel
    Protected Overrides Sub CreateChildElements()
        MyBase.CreateChildElements()
        dock = New DockLayoutPanel()
        dock.StretchHorizontally = True
        dock.LastChildFill = False
        Me.Children.RemoveAt(Me.Children.Count - 1)
        Me.Children.Add(dock)
    End Sub

    Protected Overrides Sub CalculateItems()
        Me.SuspendLayout()

        Dim cellInfo As GanttTimelineCellsInfo = Me.GraphicalViewElement.TimelineBehavior.GetTimelineCellInfoForItem(Me.Data, Me.GraphicalViewElement.TimelineRange)

        While Me.dock.Children.Count > cellInfo.NumberOfcells
            Me.dock.Children.RemoveAt(0)
        End While

        While Me.dock.Children.Count < cellInfo.NumberOfcells
            Dim element As LightVisualElement = Me.GraphicalViewElement.TimelineBehavior.CreateElement()
            Me.dock.Children.Add(element)
        End While

        Me.TopElement.Text = Me.GraphicalViewElement.TimelineBehavior.GetTimelineTopElementText(Me.Data)

        For i As Integer = 0 To Me.dock.Children.Count - 1
            DirectCast(Me.dock.Children(i), LightVisualElement).Text = Me.GraphicalViewElement.TimelineBehavior.GetTimelineBottomElementText(Me.Data, i + cellInfo.StartIndex)
        Next

        Me.ResumeLayout(True)
    End Sub

    Protected Overrides Function MeasureOverride(availableSize As SizeF) As SizeF
        Dim clientRect As RectangleF = Me.GetClientRectangle(availableSize)
        Dim width As Single = Me.Data.Width - Me.GraphicalViewElement.TimelineContainer.ItemSpacing + availableSize.Width - clientRect.Width

        Me.TopElement.Measure(New SizeF(width, clientRect.Height / 2.0F))
        Me.dock.Measure(New SizeF(width, clientRect.Height / 2.0F))

        Return New SizeF(width, Me.TopElement.DesiredSize.Height + Me.dock.DesiredSize.Height)
    End Function

    Protected Overrides Function ArrangeOverride(finalSize As SizeF) As SizeF
        Dim clientRect As RectangleF = Me.GetClientRectangle(finalSize)

        Dim topRect As New RectangleF(clientRect.X, clientRect.Y, Me.DesiredSize.Width, clientRect.Height / 2.0F)
        Me.TopElement.Arrange(topRect)
        Dim bottomRect As New RectangleF(clientRect.X, topRect.Bottom, Me.DesiredSize.Width, clientRect.Height - topRect.Height)
        Me.dock.Arrange(bottomRect)

        Return clientRect.Size
    End Function
End Class

Public Class CustomGanttViewTimelineElementProvider
Inherits GanttViewTimelineElementProvider

    Public Sub New(owner As GanttViewGraphicalViewElement)
        MyBase.New(owner)

    End Sub
    Public Overrides Function CreateElement(data As GanttViewTimelineDataItem, context As Object) As IVirtualizedElement(Of GanttViewTimelineDataItem)
        Dim element As GanttViewTimelineItemElement = Me.OnItemElementCreating(data)

        Return New CustomGanttViewTimelineItemElement(data, Owner)
    End Function
End Class

To reproduce: run the sample project and try to move a task.

Workaround:

 Timer timer = new Timer();

        private void DragDropService_Stopped(object sender, EventArgs e)
        {
            timer = new Timer();
            timer.Interval = 300;
            timer.Tick += timer_Tick;
            
        }

        private void timer_Tick(object sender, EventArgs e)
        {
            timer.Stop();
            data.Tables["Tasks"].Clear();
        }

Workaround 2:

        private void radGanttView1_ItemElementCreating(object sender, Telerik.WinControls.UI.GanttViewItemElementCreatingEventArgs e)
        {
            if (e.Item.Items.Count == 0 && e.ViewElement is GanttViewGraphicalViewElement)
            {
                e.ItemElement = new MyGanttViewTaskItemElement(e.ViewElement as GanttViewGraphicalViewElement); 
            }
        }

        public class MyGanttViewTaskItemElement : GanttViewTaskItemElement
        {
            public MyGanttViewTaskItemElement(GanttViewGraphicalViewElement ganttViewBaseViewElement) : base(ganttViewBaseViewElement)
            {
            }
            
            protected override Type ThemeEffectiveType
            {
                get
                {
                    return typeof(GanttViewTaskItemElement);
                }
            }

            public override void Detach()
            {
                var obj = this.Data;
                this.Data.SuspendPropertyNotifications();
                base.Detach();
                obj.ResumePropertyNotifications(); 
            }

            public override void Synchronize()
            {
                DataSet ds = this.Data.GanttViewElement.DataSource as DataSet;
                if (ds != null && this.Data != null)
                {
                    DataRowView rowView = this.Data.DataBoundItem as DataRowView;
                    if (rowView != null && !RowExists(rowView.Row))//!ds.Tables[0].Rows.Contains(rowView.Row))
                    {
                        return;
                    }
                }
                base.Synchronize();
            }

            private bool RowExists(DataRow dataRow)
            {
                DataSet ds = this.Data.GanttViewElement.DataSource as DataSet;
                bool res = false;
                foreach (DataRow r in ds.Tables[0].Rows)
                {
                    if (r.Equals(dataRow))
                    {
                        return true;
                    }
                }
                return res;
            }
        }

To reproduce: populate RadGanttView with data and hide some of the columns in a button's Click event: 

    Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
        Me.RadGanttView1.GanttViewElement.Columns(0).Visible = False
    End Sub

The column is not hidden until you move the splitter.

Workaround:

    Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
        Me.RadGanttView1.GanttViewElement.Columns(0).Visible = False

        Me.RadGanttView1.GanttViewElement.InvalidateMeasure(True)
        Me.RadGanttView1.GanttViewElement.UpdateLayout()
    End Sub

To reproduce:

        public RadForm1()
        {
            InitializeComponent();

            DataSet ds = new DataSet();
            DataTable dt = new DataTable();
            dt.TableName = "Tasks";
            dt.Columns.Add("Id");
            dt.Columns.Add("ParentID");
            dt.Columns.Add("Title");
            dt.Columns.Add("Start", typeof(DateTime));          
            dt.Columns.Add("End", typeof(DateTime));
            dt.Rows.Add("1", "", "Item1", new DateTime(2018,03,16), new DateTime(2018,03,20));
            dt.Rows.Add("2", "1", "child", new DateTime(2018,03,16), new DateTime(2018,03,17));
            dt.Rows.Add("3", "", "Item2", new DateTime(2018,03,16), new DateTime(2018,03,20));
            ds.Tables.Add(dt);

            this.radGanttView1.GanttViewElement.TaskDataMember = "Tasks";
            this.radGanttView1.GanttViewElement.ChildMember = "Id";
            this.radGanttView1.GanttViewElement.ParentMember = "ParentId";
            this.radGanttView1.GanttViewElement.TitleMember = "Title";
            this.radGanttView1.GanttViewElement.StartMember = "Start";
            this.radGanttView1.GanttViewElement.EndMember = "End";
            this.radGanttView1.GanttViewElement.DataSource = ds;
            this.radGanttView1.Columns.Add("Start");
            this.radGanttView1.Columns.Add("End");            
            this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineStart = new DateTime(2018,03,10);
            this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineEnd = new DateTime(2018,03,31);
            //"child" item is readonly
            radGanttView1.Items[0].ReadOnly = true; 
        }

Workaround:

        public class CustomBaseGanttViewBehavior : BaseGanttViewBehavior
        {
            protected override void ProcessMouseDownOnTaskElement(GanttGraphicalViewBaseTaskElement element, MouseEventArgs e)
            {
                GanttGraphicalViewBaseItemElement taskItem = element.Parent as GanttGraphicalViewBaseItemElement;
                
                if (e.Button == MouseButtons.Left && !taskItem.Data.ReadOnly)
                {
                    base.ProcessMouseDownOnTaskElement(element, e);
                }
            }
        }

Workaround: In the case of DateTime columns one can handle the PrintElementFormating event and change text of the print elements with the required format string
private void RadGanttView1_PrintElementFormatting(object sender, Telerik.WinControls.UI.GanttViewPrintElementFormattingEventArgs e)
{
    if (e.PrintContext == GanttViewPrintElementContext.DataCell)
    {
        DateTime date;
        if (e.PrintElement.DrawText && DateTime.TryParse(e.PrintElement.Text, out date))
        {
            e.PrintElement.Text = string.Format("{0:D}", date);
        }
    }
}

See attached video to reproduce.

Workaround:

class MyGantt : RadGanttView
{

    protected override RadGanttViewElement CreateGanttViewElement()
    {
        return new MyGanttElement();
    }
}
class MyGanttElement : RadGanttViewElement
{
    
    protected override void InitializeFields()
    {
        base.InitializeFields();
        ThemeRole = "RadGanttViewElement";
    }

    protected override bool EndEditCore(bool commitChanges)
    {
        if (this.ActiveEditor.Value == null)
        {
            GanttViewDataItem item = this.SelectedItem as GanttViewDataItem;
            this.ActiveEditor.Value = item[CurrentColumn];
           
        }
        return base.EndEditCore(commitChanges);
    }
}

How to reproduce: 
public partial class RadForm1 : Telerik.WinControls.UI.RadForm
    {
        public RadForm1()
        {
            InitializeComponent();

            this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineStart = new DateTime(2010, 10, 9);
            this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineEnd = new DateTime(2010, 12, 10);

            //setup data items
            GanttViewDataItem item1 = new GanttViewDataItem();
            item1.Start = new DateTime(2010, 10, 10);
            item1.End = new DateTime(2010, 10, 15);
            item1.Progress = 30m;
            item1.Title = "Summary task.1. title";

            GanttViewDataItem subitem11 = new GanttViewDataItem();
            subitem11.Start = new DateTime(2010, 10, 10);
            subitem11.End = new DateTime(2010, 10, 12);
            subitem11.Progress = 10m;
            subitem11.Title = "Sub-task.1.1 title";

            GanttViewDataItem subitem12 = new GanttViewDataItem();
            subitem12.Start = new DateTime(2010, 10, 12);
            subitem12.End = new DateTime(2010, 10, 15);
            subitem12.Progress = 20m;
            subitem12.Title = "Sub-task.1.2 title";

            //add subitems
            item1.Items.Add(subitem11);
            item1.Items.Add(subitem12);

            this.radGanttView1.Items.Add(item1);

            GanttViewDataItem item2 = new GanttViewDataItem();
            item2.Start = new DateTime(2010, 10, 12);
            item2.End = new DateTime(2010, 10, 18);
            item2.Progress = 40m;
            item2.Title = "Summary task.2. title";

            GanttViewDataItem subitem21 = new GanttViewDataItem();
            subitem21.Start = new DateTime(2010, 10, 12);
            subitem21.End = new DateTime(2010, 10, 13);
            subitem21.Progress = 10m;
            subitem21.Title = "Sub-task.2.1 title";

            GanttViewDataItem subitem22 = new GanttViewDataItem();
            subitem22.Start = new DateTime(2010, 10, 13);
            subitem22.End = new DateTime(2010, 10, 18);
            subitem22.Progress = 30m;
            subitem22.Title = "Sub-task.2.2 title";

            GanttViewDataItem subitem23 = new GanttViewDataItem();
            subitem23.Start = new DateTime(2010, 10, 18);
            subitem23.End = new DateTime(2010, 10, 18);
            subitem23.Title = "Sub-task.2.3 title";

            //add subitems
            item2.Items.Add(subitem21);
            item2.Items.Add(subitem22);
            item2.Items.Add(subitem23);

            this.radGanttView1.Items.Add(item2);

            //add links between items
            GanttViewLinkDataItem link1 = new GanttViewLinkDataItem();
            link1.StartItem = subitem11;
            link1.EndItem = subitem12;
            link1.LinkType = TasksLinkType.FinishToStart;
            this.radGanttView1.Links.Add(link1);

            GanttViewLinkDataItem link2 = new GanttViewLinkDataItem();
            link2.StartItem = subitem21;
            link2.EndItem = subitem22;
            link2.LinkType = TasksLinkType.StartToStart;
            this.radGanttView1.Links.Add(link2);

            GanttViewLinkDataItem link3 = new GanttViewLinkDataItem();
            link3.StartItem = subitem22;
            link3.EndItem = subitem23;
            link3.LinkType = TasksLinkType.FinishToStart;
            this.radGanttView1.Links.Add(link3);

            GanttViewTextViewColumn titleColumn = new GanttViewTextViewColumn("Title");
            GanttViewTextViewColumn startColumn = new GanttViewTextViewColumn("Start");
            GanttViewTextViewColumn endColumn = new GanttViewTextViewColumn("End");

            this.radGanttView1.GanttViewElement.Columns.Add(titleColumn);
            this.radGanttView1.GanttViewElement.Columns.Add(startColumn);
            this.radGanttView1.GanttViewElement.Columns.Add(endColumn);

            this.radGanttView1.GanttViewElement.GraphicalViewElement.TimelineStart = new DateTime(2010, 10, 13);
        }

        private void radButton1_Click(object sender, EventArgs e)
        {
            RadPrintDocument doc = new RadPrintDocument();
            doc.Landscape = true;
            RadPrintPreviewDialog dialog = new RadPrintPreviewDialog();
            doc.AssociatedObject = this.radGanttView1;
            dialog.Document = doc;
            dialog.ShowDialog();
        }
    }

Workaround: create a custom RadGanttView
public class MyRadGanttView : RadGanttView
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadGanttView).FullName;
        }
    }

    protected override PointF[] GetElementShape(GanttViewPrintElementContext context, RectangleF rect)
    {
        if (shouldPaintStartCap)
        {
            return base.GetElementShape(context, rect);
        }

        switch (context)
        {
            case GanttViewPrintElementContext.SummaryTaskElement:
                PointF[] summaryPoints = new PointF[5];
                summaryPoints[0] = rect.Location;
                summaryPoints[1] = new PointF(rect.X, rect.Y + rect.Height / 4f);
                summaryPoints[2] = new PointF(rect.Right - 3, rect.Y + rect.Height / 4f);
                summaryPoints[3] = new PointF(rect.Right, rect.Y + rect.Height / 2f);
                summaryPoints[4] = new PointF(rect.Right, rect.Y);
                
                return summaryPoints;
            case GanttViewPrintElementContext.MilestoneElement:
                PointF[] milestonePoints = new PointF[4];
                milestonePoints[0] = new PointF(rect.X, rect.Y);
                milestonePoints[1] = new PointF(rect.X + rect.Height / 2f, rect.Y + rect.Height / 2f);
                milestonePoints[2] = new PointF(rect.X, rect.Y + rect.Height);
                milestonePoints[3] = new PointF(rect.X - rect.Height / 2f, rect.Y + rect.Height / 2f);

                return milestonePoints;
            default:
                return null;
        }
    }

    private bool shouldPaintStartCap;
    protected override RectangleF GetPrintRectangle(GanttViewDataItem item, int index)
    {
        if (index < 0)
        {
            return RectangleF.Empty;
        }
        
        float x = (float)((item.Start - this.GanttViewElement.GraphicalViewElement.TimelineBehavior.AdjustedTimelineStart).TotalSeconds / this.GanttViewElement.GraphicalViewElement.OnePixelTime.TotalSeconds);
        this.shouldPaintStartCap = x > 0 ? true : false;
        x = Math.Max(x, 0);

        float y = index * (this.GanttViewElement.ItemHeight + this.GanttViewElement.ItemSpacing) + this.GanttViewElement.HeaderHeight;
        float width = (float)((item.End - item.Start).TotalSeconds / (float)this.GanttViewElement.GraphicalViewElement.OnePixelTime.TotalSeconds);

        return new RectangleF(x, y, width, (this.GanttViewElement.ItemHeight + this.GanttViewElement.ItemSpacing));
    }
}

Workaround: handle the RadGanttView.GraphicalViewItemFormatting event:

    Private Sub GraphicalViewItemFormatting(sender As Object, e As GanttViewGraphicalViewItemFormattingEventArgs)
        Dim taskItem As GanttViewTaskItemElement = TryCast(e.ItemElement, GanttViewTaskItemElement)
        If taskItem IsNot Nothing Then
            taskItem.LeftLinkHandleElement.Opacity = 0
            taskItem.RightLinkHandleElement.Opacity = 0
        End If 
    End Sub

Dim data As New DataSet()
Dim tasks As New DataTable("Tasks")
Dim links As New DataTable("Links")
Sub New()
    InitializeComponent()

    tasks.Columns.Add("Id", GetType(Integer))
    tasks.Columns.Add("ParentId", GetType(Integer))
    tasks.Columns.Add("Title", GetType(String))
    tasks.Columns.Add("Start", GetType(DateTime))
    tasks.Columns.Add("End", GetType(DateTime))
    tasks.Columns.Add("Progress", GetType(Decimal))

    links.Columns.Add("StartId", GetType(Integer))
    links.Columns.Add("EndId", GetType(Integer))
    links.Columns.Add("LinkType", GetType(Integer))

    data.Tables.Add(tasks)
    data.Tables.Add(links)
    tasks.Rows.Add(1, 0, "1. Summary task title", New DateTime(2010, 10, 10), New DateTime(2010, 10, 15), 30D)
    tasks.Rows.Add(2, 1, "1.1 Task", New DateTime(2010, 10, 10), New DateTime(2010, 10, 12), 10)
    tasks.Rows.Add(3, 1, "1.2 Task", New DateTime(2010, 10, 12), New DateTime(2010, 10, 15), 20D)
    tasks.Rows.Add(4, 1, "1.3 Task", New DateTime(2010, 10, 10), New DateTime(2010, 10, 11), 20D)
    tasks.Rows.Add(5, 1, "Milestone", New DateTime(2010, 10, 15), New DateTime(2010, 10, 15), 0D)
    tasks.Rows.Add(6, 0, "2. Summary task title", New DateTime(2010, 10, 10), New DateTime(2010, 10, 13), 30D)
    tasks.Rows.Add(7, 6, "2.1 Task", New DateTime(2010, 10, 10), New DateTime(2010, 10, 11), 10)
    links.Rows.Add(2, 3, 1)
    links.Rows.Add(3, 5, 1)

    Bind()
    Me.RadGanttView1.Columns.Add("Start")
    Me.RadGanttView1.Columns.Add("End")
    Me.RadGanttView1.Columns.Add("Id")
    Me.RadGanttView1.Columns.Add("ParentId")

    Me.RadGanttView1.GanttViewElement.GraphicalViewElement.TimelineStart = New DateTime(2010, 10, 9)
End Sub

Private Sub Bind()
    Me.RadGanttView1.GanttViewElement.DataSource = Nothing
    Me.RadGanttView1.GanttViewElement.TaskDataMember = "Tasks"
    Me.RadGanttView1.GanttViewElement.ChildMember = "Id"
    Me.RadGanttView1.GanttViewElement.ParentMember = "ParentId"
    Me.RadGanttView1.GanttViewElement.TitleMember = "Title"
    Me.RadGanttView1.GanttViewElement.StartMember = "Start"
    Me.RadGanttView1.GanttViewElement.EndMember = "End"
    Me.RadGanttView1.GanttViewElement.ProgressMember = "Progress"
    Me.RadGanttView1.GanttViewElement.LinkDataMember = "Links"
    Me.RadGanttView1.GanttViewElement.LinkStartMember = "StartId"
    Me.RadGanttView1.GanttViewElement.LinkEndMember = "EndId"
    Me.RadGanttView1.GanttViewElement.LinkTypeMember = "LinkType"
    Me.RadGanttView1.GanttViewElement.DataSource = data
End Sub

Private Sub RadButtonClick(sender As Object, e As EventArgs) Handles RadButton2.Click
    tasks(3)("ParentId") = 6
    Bind()
End Sub

Workaround: rebind the ganttview after changing the parent.

To reproduce: have a look at the attached gif file and sample project.

Workaround:

            this.radGanttView1.CursorChanged += radGanttView1_CursorChanged;
            this.radGanttView1.MouseMove += radGanttView1_MouseMove;

        private void radGanttView1_MouseMove(object sender, MouseEventArgs e)
        {
            GanttViewGraphicalViewElement view = this.radGanttView1.ElementTree.GetElementAtPoint(e.Location).FindAncestor<GanttViewGraphicalViewElement>();
            Console.WriteLine(this.radGanttView1.ElementTree.GetElementAtPoint(e.Location));
            if (view != null)
                isOverGraphicalView = true;
            else
                isOverGraphicalView = false;
        }

        bool isOverGraphicalView = false;

        private void radGanttView1_CursorChanged(object sender, EventArgs e)
        {
            if (isOverGraphicalView)
            {
                this.radGanttView1.CursorChanged -= radGanttView1_CursorChanged;
                this.radGanttView1.Cursor = Cursors.Default;
                this.radGanttView1.CursorChanged += radGanttView1_CursorChanged;
            }
        }