In the Swimlane diagram example (Data Visualization -> Diagrams -> Swimlane) the application crashes, showing at least one but often more than one error message.

How to reproduce:

• Open the Swimlane example.
• Click the area that is labelled as "Process name" (also marked in the attached screenshot)
• One or multiple Message boxes containing the exception message

{DependencyProperty.UnsetValue} is not a valid value for the Property "Background"

pop up (see other screenshot)

Arrow keys (up and down) don't scroll the first row which is outside of the viewport. One way to reproduce this is to scroll down, then select the topmost visible row and press the Up arrow key in order to select the row above. This should scroll the view a bit up in order to see the previous row which is now selected.
Currently, this doesn't work when using a custom implementation of the GridViewCell class.
The issue is reproducible when GroupRenderMode is set to Flat.

To work this around, you can manually scroll to the row.

public MainWindow()
{
	InitializeComponent();
	this.gridView.AddHandler(RadGridView.KeyUpEvent, new KeyEventHandler(OnGridViewKeyUp), true);
}

private void OnGridViewKeyUp(object? sender, System.Windows.Input.KeyEventArgs e)
{
	if (e.Key == Key.Up || e.Key == Key.Down)
	{
		Dispatcher.BeginInvoke(new Action(() =>
		{
			var currentCell = gridView.CurrentCell;
			var row = currentCell.ParentRow;

			// Since the VisualOffset proeprty is protected and you are already inheriting the GridViewRow class, you can just expose it through an extra property in the CustomGridViewRow, instead of using reflection like in this example.
			var visualOffsetPropInfo = typeof(Visual).GetProperty("VisualOffset", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic); 			
			var offset = (Vector)visualOffsetPropInfo.GetValue(row);
			if (offset.Y < 0)
			{
				row.BringIntoView();
			}
		}));
	}
}

The image adorner in is not shown in NetCore/6/7/8 when ApplicationTheme is not set (XAML only).

Workaround:

Explicitly set the theme:

 StyleManager.ApplicationTheme = new Office2016Theme();

InvalidCastException is thrown when the DropIndicatorThickness property of the GridViewHeaderCell is set. Or whenever the DropIndicatorBrush property is accessed. This happens when using the Windows 7 theme. Also, the EnableColumnVirtualization property should be set to False.

System.InvalidCastException: 'Unable to cast object of type 'System.Windows.Media.LinearGradientBrush' to type 'System.Windows.Media.SolidColorBrush'.'

To work this around, you can use an implicit style targeting the GridViewHeaderCell in order to set its DropIndicatorBrush to a SolidColorBrush value.

 <telerik:RadGridView.Resources>
     <Style TargetType="telerik:GridViewHeaderCell">
         <Setter Property="DropIndicatorBrush" Value="White" />
         <Setter Property="DropIndicatorThickness" Value="10" />
     </Style>
 </telerik:RadGridView.Resources>

When the Expression_Dark theme is applied to the RadPropertyGrid, selecting an item is hard to read, as the item's foreground is white and the selection state is in a similar color.

To work this around, use the following Style:

<Style TargetType="telerik:PropertyGridField">
    <Style.Triggers>
        <Trigger Property="IsSelected" Value="True">
            <Setter Property="Foreground" Value="Black"/>
        </Trigger>
    </Style.Triggers>
</Style>

An ObjectDisposedException exception is raised when a RadSvgImage is placed in a DataTemplate. It is present when the XmlSource property is utilized.

As a workaround, you can place the SVG string into a new .svg file and utilize the UriSource property of RadSvgImage.

The fly view is not properly displayed when the second item is clicked and the sub-items are expanded (see attached video). 

Attached is a project with a workaround as well. 

InvalidOperationException when closing a RadWindow opened on a separated UI thread. The exception message is: "Cannot use a DependencyObject that belongs to a different thread than its parent Freezable."

To work this around, you can merge the Telerik.Windows.Controls.Navigation.xaml dictionary in the Resources of all RadWindow instances open on another thread and then set their Style property to the RadWindowStyle from the merged .xaml dictionary.

<telerik:RadWindow x:Class="WpfApp84.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp84" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
        mc:Ignorable="d"  Height="450" Width="800" Style="{DynamicResource RadWindowStyle}">
    <telerik:RadWindow.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/Telerik.Windows.Controls.Navigation;component/Themes/GenericWindows11.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </telerik:RadWindow.Resources>
</telerik:RadWindow>

Column groups may disappear when the RadGridView control is hosted in a TabItem of TabControl. These column groups can disappear when new GridViewColumnGroup instances are created.

Furthermore, resizing a column of RadGridView will result in a NullReferenceException.

To work this around, set the EnableColumnGroupsVirtualization property of RadGridView to False.