Use attached to reproduce. 

Workaround
radPropertyGrid1.ItemSpacing = 1;

To reproduce:

            this.radPropertyGrid1.SelectedObject = this;             
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.MinSize = new Size(0, 60);

Please refer to the attached gif file.

Workaround:

            this.radPropertyGrid1.SelectedObject = this;             
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.MinSize = new Size(0, 60);
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpTitleElement.MinSize = new Size(0,20);

            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpTitleElement.PropertyChanged += HelpTitleElement_PropertyChanged;

        private void HelpTitleElement_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == "Bounds")
            {
                if (this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpContentElement.Location.Y != 20)
                {
                    this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpContentElement.Location = new Point(0, 20);
                }
            }
        }

Note: the description element may be floating but it doesn't overlap the title. 

How to reproduce: associate the control with an object having a Font property. It can be the form itself, then try and change the font-size, e.g: -1.

The standard property grid displays a message box with the error.

Workaround handle the RadPropertyGrid.EditorInitialized event:
private void RadPropertyGrid_EditorInitialized(object sender, PropertyGridItemEditorInitializedEventArgs e)
{
    PropertyGridSpinEditor editor = e.Editor as PropertyGridSpinEditor;
    if (editor != null && e.Item.Parent != null && e.Item.Parent.Name == "Font" && e.Item.Name == "Size")
    {
        editor.MinValue = 1;
    }
}

Use the editor from the following article to reproduce: https://docs.telerik.com/devtools/winforms/propertygrid/editors/using-custom-editor

Workaround:
void TrackBarEditor_ValueChanged(object sender, EventArgs e)
{
    PropertyGridItemElement owner = this.OwnerElement as PropertyGridItemElement;

    if (owner != null)
    {
        var method = owner.PropertyTableElement.GetType().GetMethod("OnValueChanged", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        method.Invoke(owner.PropertyTableElement, new object[] { this, EventArgs.Empty });

    }
}

Use attached project to reproduce!
This works fine in  2016.2.608.

Workaround:
Use singe RadPropertyStore object instead of an array.

To reproduce: subscribe to the RadPropertyGrid.PropertyValidating event and apply ErrorMessage in some cases. If the validation fails, the error indicator is not visible in Windows8, VisualStudio2012Dark, Aqua. However, the error message is displayed as expected.

Workaround: assign an image for the ErrorIndicator

private void radPropertyGrid1_ItemFormatting(object sender, PropertyGridItemFormattingEventArgs e)
{
    PropertyGridItemElement itemElement = e.VisualElement as PropertyGridItemElement;
    if (itemElement != null)
    {
        ((PropertyGridTextElement)itemElement.TextElement).ErrorIndicator.Image = Properties.Resources.error;
    }
}

Add the ReadOnly flag to true at the property of custom TestClass.
If you select a single object the this property is ReadOnly but if you select more than one objects it isn't ReadOnly anymore.

select two items in the grid, click on the ValueI in the MS GridView then press ESC and click again on ValueI: the cell is always empty.
Do the same thing in your RadPropertyGrid. The first time you get 0, the second time -2147483648.

I have problem with your default PropertyGridDropDownListEditor. When the dropdown initially appears at 175% scaling, there's excessive empty space at the bottom of the values list.

To reproduce:

PropertyStoreItem prop1 = new PropertyStoreItem(typeof(DateTime), "Date", DateTime.Now);
PropertyStoreItem prop2 = new PropertyStoreItem(typeof(Nullable<DateTime>), "NullableDate", DateTime.Now);
PropertyStoreItem prop3 = new PropertyStoreItem(typeof(DateTime?), "Date?", DateTime.Now);

RadPropertyStore store = new RadPropertyStore();
store.Add(prop1);
store.Add(prop2);
store.Add(prop3); 
this.radPropertyGrid1.SelectedObject = store;

Open the editor for one of the properties and press the Clear button in the PropertyGridDateTimeEditor's popup. The value is cleared, but the PropertyValueButtonElement is not displayed.

Workaround: specify the initial value as default value for the property:

public Form1()
{
    InitializeComponent();

    DateTime initialValue = DateTime.Now;
    PropertyStoreItem prop1 = new PropertyStoreItem(typeof(DateTime), "Date", initialValue);
    prop1.Attributes.Add(new DefaultValueAttribute(initialValue));
    PropertyStoreItem prop2 = new PropertyStoreItem(typeof(Nullable<DateTime>), "NullableDate", initialValue);
    prop2.Attributes.Add(new DefaultValueAttribute(initialValue));
    PropertyStoreItem prop3 = new PropertyStoreItem(typeof(DateTime?), "Date?", initialValue);
    prop3.Attributes.Add(new DefaultValueAttribute(initialValue));
    
    RadPropertyStore store = new RadPropertyStore();
    store.Add(prop1);
    store.Add(prop2);
    store.Add(prop3); 
    this.radPropertyGrid1.SelectedObject = store;
     
}

Workaround: set the RadPropertyGrid.SelectedGridItem property to null before changing the SelectedObject.

To reproduce: 

1. Add a RadPropertyGrid and populate it with all of of  items by using the following code:
                      this.radPropertyGrid1.SelectedObject = this;
2. Expand two items.
3. Scroll to the bottom.
4. Scroll to the top.
5. If you scroll to the bottom again, you will see a lot of empty space. The attached gif file illustrates better the problem.

Workaround:
public Form1()
{
    InitializeComponent();

    this.radPropertyGrid1.SelectedObject = this;
    this.radPropertyGrid1.PropertyGridElement.PropertyTableElement.Scroller.Traverser =
        new CustomPropertyGridTraverser(this.radPropertyGrid1.PropertyGridElement.PropertyTableElement);
}

public class CustomPropertyGridTraverser : PropertyGridTraverser
{
    public CustomPropertyGridTraverser(PropertyGridTableElement propertyGridElement) : base(propertyGridElement)
    {
    }

    public int Index
    {
        get
        {
            FieldInfo fi = typeof(PropertyGridTraverser).GetField("index", BindingFlags.NonPublic | BindingFlags.Instance);
            return int.Parse(fi.GetValue(this).ToString());
        }
        set 
        {
            FieldInfo fi = typeof(PropertyGridTraverser).GetField("index", BindingFlags.NonPublic | BindingFlags.Instance);
            fi.SetValue(this, value);
        }
    }

    public int GroupIndex
    {
        get
        {
            FieldInfo fi = typeof(PropertyGridTraverser).GetField("groupIndex", BindingFlags.NonPublic | BindingFlags.Instance);
            return int.Parse(fi.GetValue(this).ToString());
        }
    }

    public PropertyGridTableElement Element
    {
        get
        {
            FieldInfo fi = typeof(PropertyGridTraverser).GetField("propertyGridElement", BindingFlags.NonPublic | BindingFlags.Instance);
            return fi.GetValue(this) as PropertyGridTableElement ;
        }
    }

    public PropertyGridItemBase Item
    {
        get
        {
            FieldInfo fi = typeof(PropertyGridTraverser).GetField("item", BindingFlags.NonPublic | BindingFlags.Instance);
            return fi.GetValue(this) as PropertyGridItemBase ;
        }
        set 
        {
            FieldInfo fi = typeof(PropertyGridTraverser).GetField("item", BindingFlags.NonPublic | BindingFlags.Instance);
            fi.SetValue(this, value);
        }
    }

    protected override bool MovePreviousFromDataItem(PropertyGridItemBase currentItem)
    {
        if (currentItem.Parent != null && currentItem.Parent.GridItems.Count > 0)
        {
            if (this.Index > 0)
            {
                PropertyGridItemBase prevItem = currentItem.Parent.GridItems[--this.Index];
                if (prevItem.Expandable && (prevItem.Expanded || this.TraverseHirarchy))
                {
                    prevItem = this.GetLastChild(prevItem);
                }

                this.Item = prevItem;
                return true;
            }

            this.Item = currentItem.Parent;
            this.Index = -1;
            if (currentItem.Parent.Parent != null)
            {
                this.Index = currentItem.Parent.Parent.GridItems.IndexOf(currentItem.Parent as PropertyGridItem);
            }
            else
            {
                if (this.Element.CollectionView.Groups.Count == 0)
                {
                    this.Index = this.Element.CollectionView.IndexOf(currentItem.Parent as PropertyGridItem);
                }
                else
                {
                    this.Index = this.Element.CollectionView.Groups[this.GroupIndex].IndexOf(currentItem.Parent as PropertyGridItem);
                }
            }
            return true;
        }
        return base.MovePreviousFromDataItem(currentItem);
    }
}

The PropertyChanged event does not fire when the ValueColumnWidth property is changed.

To reproduce: 
private void PopulateGrid()
{
    this.radPropertyGrid1.SortOrder = System.Windows.Forms.SortOrder.Ascending;
    PropertyStoreItem myRadProp;
  
    RadPropertyStore myRadProperties = new RadPropertyStore();

    for (int i = 0; i <= 6000; i++)
    {

        myRadProp = new PropertyStoreItem(typeof(string), "PropName" + i, "Value" + i, "Help" + i, "same");

        myRadProperties.Add(myRadProp);
    }

    radPropertyGrid1.SelectedObject = myRadProperties;
}


Workaround:

public Form1()
{
    InitializeComponent();

    radPropertyGrid1.PropertyGridElement.PropertyTableElement.ListSource.CollectionView.GroupFactory =
        new MyPropertyGridGroupFactory(this.radPropertyGrid1.PropertyGridElement.PropertyTableElement);
    this.radPropertyGrid1.SortOrder = System.Windows.Forms.SortOrder.Ascending;
    PropertyStoreItem myRadProp;

    RadPropertyStore myRadProperties = new RadPropertyStore();

    for (int i = 0; i <= 6000; i++)
    {
        myRadProp = new PropertyStoreItem(typeof(string), "PropName" + i, "Value" + i, "Help" + i, "same");

        myRadProperties.Add(myRadProp);
    }
           
    this.radPropertyGrid1.PropertyGridElement.PropertyTableElement.ListSource.BeginUpdate();
    radPropertyGrid1.SelectedObject = myRadProperties;
    this.radPropertyGrid1.PropertyGridElement.PropertyTableElement.ListSource.EndUpdate();
}

public class MyPropertyGridGroupFactory : IGroupFactory<PropertyGridItem>
{
    private PropertyGridTableElement propertyGridElement;

    public MyPropertyGridGroupFactory(PropertyGridTableElement propertyGridElement)
    {
        this.propertyGridElement = propertyGridElement;
    }

    public GroupCollection<PropertyGridItem> CreateCollection(IList<Group<PropertyGridItem>> list)
    {
        return new PropertyGridGroupCollection(list);
    }

    public Group<PropertyGridItem> CreateGroup(object key, Group<PropertyGridItem> parent, params object[] metaData)
    {
        return new MyPropertyGridGroup(key, parent, this.propertyGridElement);
    }
}

public class MyPropertyGridGroup : PropertyGridGroup
{
    private List<PropertyGridItem> items;

    public MyPropertyGridGroup(object key, Group<PropertyGridItem> parent, 
        PropertyGridTableElement propertyGridElement) : base(key, parent, propertyGridElement)
    {
    }

    protected override IList<PropertyGridItem> Items
    {
        get
        {
            if (this.items == null)
            {
                this.items = new List<PropertyGridItem>();
            }

            return this.items;
        }
    }
}

To reproduce:
 radPropertyGrid1.SelectedObject = new RadDropDownList();

The Items collection does not have a setter, but one still should be able to add items via the respective editor.

To reproduce:

public Form1()
{
    InitializeComponent();

    this.radPropertyGrid1.SelectedObject = new Item(123, "SampleName");
}

public class Item
{
    public int Id { get; set; }
    public string Name { get; set; }

    public Item(int id, string name)
    {
        this.Id = id;
        this.Name = name;
    }
}

Activate the editor for the "Id" property and click the up arrow of the PropertyGridSpinEditor. Then click on the text box.

Workaround:

private void radPropertyGrid1_EditorInitialized(object sender, PropertyGridItemEditorInitializedEventArgs e)
{
    PropertyGridSpinEditor spinEditor = e.Editor as PropertyGridSpinEditor ;
    if (spinEditor != null)
    {
        BaseSpinEditorElement spinEditorElement = spinEditor.EditorElement as BaseSpinEditorElement;
        var eventInfo = spinEditorElement.TextBoxItem.HostedControl.GetType().GetEvent("MouseEnter");
        var methodInfo = spinEditorElement.TextBoxItem.GetType().GetMethod("TextBoxControl_MouseEnter",
            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        Delegate handler = Delegate.CreateDelegate(typeof(EventHandler), spinEditorElement.TextBoxItem, methodInfo);
        eventInfo.RemoveEventHandler(spinEditorElement.TextBoxItem.HostedControl, handler);

        var eventInfo2 = spinEditorElement.TextBoxItem.HostedControl.GetType().GetEvent("MouseLeave");
        var methodInfo2 = spinEditorElement.TextBoxItem.GetType().GetMethod("textBoxItem_MouseLeave",
            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        Delegate handler2 = Delegate.CreateDelegate(typeof(EventHandler), spinEditorElement.TextBoxItem, methodInfo2);
        eventInfo2.RemoveEventHandler(spinEditorElement.TextBoxItem.HostedControl, handler2);
    }
}

To reproduce:
- Add 20 document windows that contain property grid to a dock (use RadTextBox for he grid's selected object).
- Close and dispose the windows.
- The memory is not properly released.

To reproduce:
1. Add a RadPropertyGrid and a RadButton.
2. Create custom PropertyGridItemElement with custom PropertyGridValueElement in order to display permanently RadDropDownListElement
3. Use the following code snippet:

public Form1()
{
    InitializeComponent();

    this.radPropertyGrid1.CreateItemElement += radPropertyGrid1_CreateItemElement;
    this.radPropertyGrid1.Editing += radPropertyGrid1_Editing;
}

private void radPropertyGrid1_Editing(object sender,
    PropertyGridItemEditingEventArgs e)
{
    if (e.Item.Name == "Direction")
    {
        e.Cancel = true;
    }
}

private void radPropertyGrid1_CreateItemElement(object sender,
    CreatePropertyGridItemElementEventArgs e)
{
    PropertyGridItem item = (PropertyGridItem)e.Item;
    if (e.Item.Name == "Direction")
    {
        e.ItemElementType = typeof(CustomItemElement);
    }
}

public class CustomItemElement : PropertyGridItemElement
{
    protected override PropertyGridValueElement CreatePropertyGridValueElement()
    {
        return new CustomPropertyGridValueElement();
    }

    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(PropertyGridItemElement);
        }
    }
}

public class CustomPropertyGridValueElement : PropertyGridValueElement
{
    RadDropDownListElement dropdown;

    protected override void CreateChildElements()
    {
        base.CreateChildElements();
 
        dropdown = new RadDropDownListElement();
        dropdown.DropDownStyle = Telerik.WinControls.RadDropDownStyle.DropDownList;
        this.Children.Add(dropdown);

        dropdown.DataSource = Enum.GetValues(typeof(Direction));
        dropdown.SelectedIndexChanged += dropdown_SelectedIndexChanged;
    }

    private void dropdown_SelectedIndexChanged(object sender,
        Telerik.WinControls.UI.Data.PositionChangedEventArgs e)
    {
        RadDropDownListElement ddle = sender as RadDropDownListElement;
        if (ddle != null && e.Position > -1)
        {
            PropertyGridItem item = this.VisualItem.Data as PropertyGridItem;
            if (item != null)
            {
                item.Value = ddle.Items[e.Position].DataBoundItem;
            }
        }
    }

    public override void Synchronize()
    {
        PropertyGridItem item = this.VisualItem.Data as PropertyGridItem;
        dropdown.SelectedValue = item.Value;
    }
}

public class Item
{
    public int Id { get; set; }

    public Direction Direction { get; set; }

    public string Title { get; set; }

    public Item(int id, string title, Direction direction)
    {
        this.Id = id;
        this.Title = title;
        this.Direction = direction;
    }
}

public enum Direction
{
    Up,
    Down,
    Left,
    Right
}

private void radButton1_Click(object sender, EventArgs e)
{
    this.radPropertyGrid1.SelectedObject = new Item(123, "Title", Direction.Left);
}

When you click the button once, the RadPropertyGrid displays the desired data. However, if you click the button once again, ArgumentOutOfRangeException occurs.

Workaround:wrap setting the SelectedObject in a SuspendLayout/ResumeLayout block:

this.radPropertyGrid1.SuspendLayout();
this.radPropertyGrid1.SelectedObject = new Item(123, "Title", Direction.Left);
this.radPropertyGrid1.ResumeLayout();

To reproduce:

Set the following object as selected of RadPropertyGrid: 

class TestClass : System.ComponentModel.INotifyPropertyChanged
{
    private string loggingType = "0";

    [TypeConverter(typeof(CustomListConverter)), CategoryAttribute("Logging Settings")]
    public string LoggingType
    {
        get { return loggingType; }
        set
        {
            loggingType = value;
            OnPropertyChanged("LoggingType");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public virtual void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

}

And use the following converter:

public class CustomListConverter : System.ComponentModel.StringConverter
{
    ArrayList _AllStringValues = new ArrayList();
    Hashtable _Map = new Hashtable();

    public CustomListConverter()
    {
    }

    public override System.ComponentModel.TypeConverter.StandardValuesCollection GetStandardValues(ITypeDescriptorContext conte
    {
        FillValuesFromContext();
        StandardValuesCollection standardValues = new StandardValuesCollection(_AllStringValues);
        return standardValues;
    }

    private void FillValuesFromContext()
    {
        if (_AllStringValues.Count > 0)
            return;

        _AllStringValues.Clear();
        _Map.Clear();

        string str = "-5,Fatal|-4,Error|-3,Warning|-2, Info|-1,Debug|0,Trace";

        string[] strMapVals = str.Split('|');
        for (int i = 0; i < strMapVals.Length; i++)
        {
            string[] strVals = strMapVals[i].Split(',');
            if (strVals.Length != 2)
                continue;

            _AllStringValues.Add(strVals[0].Trim());
            _Map.Add(strVals[0].Trim(), strVals[1].Trim());
        }
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        FillValuesFromContext();

        string displayString = "";

        IEnumerator enumTable = _Map.Keys.GetEnumerator();

        while (enumTable.MoveNext())
        {
            if (_Map[enumTable.Current] as string == value as string)
            {
                displayString = enumTable.Current as string;
                break;
            }
        }

        return displayString;
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        FillValuesFromContext();

        if (null != value && _Map.ContainsKey(value.ToString()))
        {
            return _Map[value];
        }

        return value;
    }

    public override bool GetStandardValuesSupported(ITypeDescriptorContext context)
    {
        return true;
    }

    public override bool GetStandardValuesExclusive(ITypeDescriptorContext context)
    {
        return true;
    }
}

When you start the application you will see that the value of the property is set to -1, while it should be converted to 'Debug'

Workaround:

Create a custom PropertyGridItem:

public class MyPropertyGridItem : PropertyGridItem
{
    public MyPropertyGridItem(PropertyGridTableElement element)
        : base(element)
    {
    }

    public override string FormattedValue
    {
        get
        {
            string baseFormattedValue =  base.FormattedValue;
            TypeConverter converter = TypeConverter;

            if (converter != null && converter.CanConvertTo(this, typeof(string)))
            {
                baseFormattedValue = converter.ConvertToString(this, System.Threading.Thread.CurrentThread.CurrentCulture, this.Value);
            }

            return baseFormattedValue;
        }
        set
        {
            base.FormattedValue = value;
        }
    }
}

Use it by subscribing to the CreateItem event:

void radPropertyGrid1_CreateItem(object sender, Telerik.WinControls.UI.CreatePropertyGridItemEventArgs e)
{
    e.Item = new MyPropertyGridItem(this.radPropertyGrid1.PropertyGridElement.PropertyTableElement);
}

To reproduce:
1. Add a RadPropertyGrid and use the following code:


public partial class NewTestWindow : Form
{
    public NewTestWindow()
    {
        InitializeComponent();


        PropertyGridData data = new PropertyGridData();
        (data as INotifyPropertyChanged).PropertyChanged += NewTestWindow_PropertyChanged;


        ppgItems.SelectedObject = data;


        Type type = ppgItems.SelectedObject.GetType();
        MemberInfo[] members = type.GetMembers();
        foreach (MemberInfo m in members)
        {
            Attribute[] attributes = Attribute.GetCustomAttributes(m);
            foreach (Attribute attr in attributes)
            {
                if (attr is BrowsableCondition)
                {
                    BrowsableCondition condition = attr as BrowsableCondition;
                    PropertyGridItem gridItem = ppgItems.Items[m.Name];


                    gridItem.Visible = false;
                }
            }
        }
    }


    private void NewTestWindow_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (ppgItems.SelectedObject != null)
        {
            PropertyInfo enableProperty = ppgItems.SelectedObject.GetType().GetProperty(e.PropertyName);
            bool? value = enableProperty.GetValue(ppgItems.SelectedObject, null) as bool?;


            if (value.HasValue)
            {
                Type type = ppgItems.SelectedObject.GetType();
                MemberInfo[] members = type.GetMembers();
                foreach (MemberInfo m in members)
                {
                    Attribute[] attributes = Attribute.GetCustomAttributes(m);
                    foreach (Attribute attr in attributes)
                    {
                        if (attr is BrowsableCondition)
                        {
                            BrowsableCondition condition = attr as BrowsableCondition;
                            PropertyGridItem gridItem = ppgItems.Items[m.Name];


                            gridItem.Visible = value.Value;
                        }
                    }
                }
            }
        }


        ppgItems.PropertyGridElement.PropertyTableElement.Update(PropertyGridTableElement.UpdateActions.Resume);
    }
}


public class PropertyGridData : INotifyPropertyChanged
{
    public string Item { get; set; }


    [Browsable(true)]
    [BrowsableCondition("Enable")]
    public bool A0 { get; set; }


    [Browsable(true)]
    [BrowsableCondition("Enable")]
    public bool A1 { get; set; }


    [Browsable(true)]
    [BrowsableCondition("Enable")]
    public bool A2 { get; set; }


    [Browsable(true)]
    [BrowsableCondition("Enable")]
    public bool A3 { get; set; }


    [Browsable(true)]
    [BrowsableCondition("Enable")]
    public bool A4 { get; set; }


    [Browsable(true)]
    [BrowsableCondition("Enable")]
    public bool A5 { get; set; }


    public string Anything { get; set; }


    private bool _enable;


    public bool Enable
    {
        get
        {
            return _enable;
        }


        set
        {
            _enable = value;
            RaisePropertyChanged("Enable");
        }
    }


    public event PropertyChangedEventHandler PropertyChanged;


    public void RaisePropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}


public class BrowsableCondition : Attribute
{
    public BrowsableCondition(string propertyName)
    {
        this.PropertyName = propertyName;
    }


    public string PropertyName { get; set; }
}


2. Run the application. The RadPropertyGrid has a checkbox with Enable property.
When selected, other properties are displayed (A0, A1, A2, A3, A4, A5). When the user marks some of these checkboxes that were hidden and then uncheck the Enable property, the PropertyGridItemElement component throws a System.NullReferenceException.