System.ArgumentException: 'An item with the same key has already been added.' when the data source contains DateTime with the same hour, minute, and seconds part (only milliseconds are different):

In this case, the RadGridView AutoSizeRows and ColumnGroupViewDefinition are enabled. The rows will have different heights depending on the cell content. When exporting the RadGridView to PDF, the rows will have equal size and won't respect the current size in the view. Thus longer text in a cell will be cut off. 

The same behavior is observed when exporting to PDF or XLSX. In addition, this is also observed when printing the RadGridView.

The following line gets serialized when set this property:

((Telerik.WinControls.UI.GridSelectCheckBoxElement)(this.radGridView1.GetChildAt(0).GetChildAt(0).GetChildAt(2).GetChildAt(0).GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(1).GetChildAt(0))).Visibility = Telerik.WinControls.ElementVisibility.Collapsed;

Incorrect or missing accessible object names in the Inspect.exe tool (MSAA).

Call stack:

Telerik.WinControls.GridView.dll!Telerik.WinControls.UI.GridGroupHeaderRowElement.Initialize(Telerik.WinControls.UI.GridViewRowInfo rowInfo) Line 100
	at Telerik.WinControls.UI\GridGroupHeaderRowElement.cs(100)
Telerik.WinControls.GridView.dll!Telerik.WinControls.Export.GridExportUtils.GetRowHeight(Telerik.WinControls.UI.RadGridView radGridView, Telerik.WinControls.UI.RowElementProvider rowProvider, Telerik.WinControls.UI.CellElementProvider cellProvider, Telerik.WinControls.UI.GridViewRowInfo gridViewRowInfo, bool exportVisualSettings) Line 158
	at Telerik.WinControls.Export\GridExportUtils.cs(158)
Telerik.WinControls.GridView.dll!Telerik.WinControls.Export.GridViewSpreadExport.AddRow(Telerik.WinControls.UI.GridViewRowInfo gridViewRowInfo, int rowIndex) Line 960

Run the attached project on a monitor with 100% DPI scaling and open the Excel-like filter popup:

100%:

After moving the form to the second monitor with 150% DPI scaling, the filter popup is not OK:

150%:

The popup is smaller and smaller with each next opening (see the attached gif file) at 150%. If you decide to move back the form on the monitor with 100% DPI scaling, the filter popup is not scaled properly.

ConditionalFormatting dialog elements are overlapping in the Windows 11 theme. The text is clipped on the right:

Load-On-Demand self-reference hierarchy provider