1. Create a new project and add RadMultiColumnComboBox
2. Bind it and setup filtering
3. Attach to SelectedValueChanged and SelectedIndexChanged events
4. Run the project
5. Apply some filtering and you will see that these events will not fire, regardless that the current row has changed.

Work around it by using the EditorControl.CurrentRowChanged event instead of SelectedValueChanged/SelectedIndexChanged events. 

To reproduce:

DataTable dt = new DataTable();
for (int i = 0; i < 10; i++)
{
    dt.Columns.Add("Column " + i);
}
for (int i = 0; i < 1000; i++)
{
    dt.Rows.Add(i);
}

this.radMultiColumnComboBox1.DataSource = dt;
this.radMultiColumnComboBox1.DisplayMember = "Column 0";
this.radMultiColumnComboBox1.DropDownSizingMode = SizingMode.UpDown;
this.radMultiColumnComboBox1.AutoSizeDropDownToBestFit = true;
this.radMultiColumnComboBox1.EditorControl.LoadElementTree();
this.radMultiColumnComboBox1.MultiColumnComboBoxElement.DropDownAnimationEnabled = false;
this.radMultiColumnComboBox1.MultiColumnComboBoxElement.ShowPopup();


The columns are autosized but the popup is not sized correctly.

When filtering is applied to RadMultiColumnComboBox editor in CellEditorInitialized event of RadGridView, the selected item is second one, if the new row is edited.

Workaround: change the event handler by adding the following lines of code in the end of the RadGridView1_CellEditorInitialized:

Dim value As Object = e.Row.Cells(e.ColumnIndex).Value
 
If value Is Nothing Then
    editor.EditorControl.CurrentRow = Nothing
Else
    editor.Value = e.Row.Cells(e.ColumnIndex).Value
End If

Use the following code and try to scroll item by item with the mouse wheel:

        public RadForm1()
        {
            InitializeComponent();

            DataTable dt = new DataTable();
            dt.Columns.Add("Id", typeof(int));
            dt.Columns.Add("Name", typeof(string));
            for (int i = 0; i < 20; i++)
            {
                dt.Rows.Add(i, "Item"+i);
            }
            this.radMultiColumnComboBox1.DisplayMember = "Name";
            this.radMultiColumnComboBox1.ValueMember = "Id";
            this.radMultiColumnComboBox1.DataSource = dt;
            this.radMultiColumnComboBox1.ScrollOnMouseWheel = true;
            this.radMultiColumnComboBox1.SelectedValueChanged+=radMultiColumnComboBox1_SelectedValueChanged;
        }

        private void radMultiColumnComboBox1_SelectedValueChanged(object sender, EventArgs e)
        {
            Console.WriteLine("Value: "+this.radMultiColumnComboBox1.SelectedValue);
        }

Expected behavior: one item is scrolled at a time

Actual behavior: two items are scrolled at a time

Note: RadDropDownList behaves as expected.

Use attached to reproduce.

Populate RadMultiColumnComboBox with data and enable the auto filter functionality. Apply a CompositeFilterDescriptor with two text columns. Try to filter entering several letters and press Tab. You will notice that the SelectedIndexChanged event is not fired in this case. However, if only one FilterDescriptor is added, not a CompositeFilterDescriptor, the selection will be properly updated. 

Please refer to the attached sample project and gif file which illustrates the behavior. 

Hello,

I'm facing a problem with the MulticolumnCombobox that results in an SelectedValueChanged-Event when the list is dropped down the first time after data source was set. Please use the attached project for reproducing the problem using the following steps:

1. Start Application on Windows 10 Chinese (Note: The described behaviour will not occur for other cultures (i.e. German will not fire the event at that time))
2. Click the Button having the Text "RadButton1", which will set the DataSource and fire the event "SelectedValueChanged" (MessageBox will pop up) which is okay at this point.
3. Now perform the drop down for the Combobox. Using Windows 10 Chinese will fire "SelectedValueChanged" and Windows 10 German will not fire "SelectedValueChanged".
   

==> As the MulticolumnCombobox performs different based on the culture, this seems to be a bug.

If you need further information, please do not hestitate to ask.

Currently, in RadMultiColumnComboBox, if you AutoFilter by all columns and you type a value that resides in the ID column, while the DisplayMember is the Name, pressing the Enter after typing the ID will return the Name in the textbox part which may be confusing to the user. Such a case may be solved by introducing another textbox in the drop-down part just for filtering purposes.

Currently RadMultiColumnComboBox uses exact comparison and it is not possible to change this behavior.

To reproduce:
Type "Th" into the multi-column combo box in the attached project.  Then press and hold the Backspace key until "Th" is deleted.  Then release Backspace key.  There remain only the filtered options in the dropdown.
If I press and release the backspace key 1x for each typed letter, then the dropdown repopulates as expected.

Workaround: 
 private void radMultiColumnComboBox1_TextChanged(object sender, EventArgs e)
        {
            this.radMultiColumnComboBox1.MultiColumnComboBoxElement.ApplyFilter();
        }

When you enable the popup sizing functionality, the last user defined size by the sizing grip should be kept.

To reproduce:
radMultiColumnComboBox.AutoFilter = True

Dim filter As New Telerik.WinControls.Data.FilterDescriptor()
filter.PropertyName = radMultiColumnComboBox.DisplayMember
filter.Operator = Telerik.WinControls.Data.FilterOperator.StartsWith

radMultiColumnComboBox.EditorControl.MasterTemplate.FilterDescriptors.Add(filter)
radMultiColumnComboBox.MultiColumnComboBoxElement.AutoCompleteMode = AutoCompleteMode.SuggestAppend
radMultiColumnComboBox.MultiColumnComboBoxElement.LimitToList = True

- Select an item, copy the text and then try to paste it.

To reproduce:
- Start the attached project and type a value so one item remains in the drop down.
- Press Enter - event is not fired.

Workaround:
Use the DropDownClosed event and check if the value is changed. 

To reproduce:

DataTable dt = new DataTable();
dt.Columns.Add("Id", typeof(int));
dt.Columns.Add("Name", typeof(string));
for (int i = 0; i < 1; i++)
{
    dt.Rows.Add(i, "Item" + i);
}
this.radMultiColumnComboBox1.DataSource = dt;
this.radMultiColumnComboBox1.DisplayMember = "Name";
this.radMultiColumnComboBox1.ValueMember = "Id";

this.radMultiColumnComboBox1.AutoFilter = true;
this.radMultiColumnComboBox1.SelectedIndex = -1;

NOTE: If you add more than 1 items, the text won't be changed.

Workaround:

Public Class CustomRadMultiColumnComboBox
Inherits RadMultiColumnComboBox
    Protected Overrides Function CreateMultiColumnComboBoxElement() As RadMultiColumnComboBoxElement
        Return New CustomRadMultiColumnComboBoxElement()
    End Function

    Public Overrides Property ThemeClassName As String
        Get
            Return GetType(RadMultiColumnComboBox).FullName
        End Get
        Set(value As String)
            MyBase.ThemeClassName = value
        End Set
    End Property
End Class

Public Class CustomRadMultiColumnComboBoxElement
Inherits RadMultiColumnComboBoxElement
    Protected Overrides Sub CheckForCompleteMatchAndUpdateText()

    End Sub
    Protected Overrides ReadOnly Property ThemeEffectiveType() As Type
        Get
            Return GetType(RadMultiColumnComboBoxElement)
        End Get
    End Property
End Class

To reproduce:
- The attached video shows how you can reproduce the issue

Note - you should type fast in the drop down and the size is invalid only the firs time.

Workaround:
RadMultiColumnComboBox1.MultiColumnComboBoxElement.DropDownAnimationEnabled = False

To reproduce:
 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            Random r = new Random();
            DataTable table = new DataTable();
            table.Columns.Add("ID", typeof(int));
            table.Columns.Add("Name", typeof(string));

            for (int i = 0; i < 10; i++)
            {
                table.Rows.Add(i, "Row with longer value " + i);
            }

            radMultiColumnComboBox1.DropDownOpening += radMultiColumnComboBox1_DropDownOpening;
            radMultiColumnComboBox1.AutoSizeDropDownToBestFit = true;
            radMultiColumnComboBox1.DataSource = table;
        }

        void radMultiColumnComboBox1_DropDownOpening(object sender, CancelEventArgs args)
        {
         //  radMultiColumnComboBox1.BestFitColumns();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Random r = new Random();
            DataTable table = new DataTable();
            table.Columns.Add("ID", typeof(int));
            table.Columns.Add("Name", typeof(string));

            for (int i = 0; i < 10; i++)
            {
                table.Rows.Add(i, "Row " + i);
            }

            radMultiColumnComboBox1.DataSource = table;

        }
    }

WORKAROUND: call the BestFitColumns method in the DropDownOpening event

Workaround:

radMultiColumnComboBox1.DropDownOpening += new RadPopupOpeningEventHandler(radMultiColumnComboBox1_DropDownOpening);
....
 void radMultiColumnComboBox1_DropDownOpening(object sender, CancelEventArgs args)
        {
            int width = 0;
            foreach (GridViewDataColumn col in radMultiColumnComboBox1.EditorControl.Columns)
            {
                width += col.Width;
            }
            radMultiColumnComboBox1.MultiColumnComboBoxElement.MultiColumnPopupForm.MinimumSize = new Size(width, 0);
             
        }