Thank you for writing.
We had a similar issue logged it in our feedback portal. However, the fix was introduced in Q3 2014
(2014.3.1104). Here is the feedback item for your reference.
version, you can use the following solution:
sender, Telerik.WinControls.UI.GridViewCellEventArgs e)
RadDropDownListEditor ddl = e.ActiveEditor
RadDropDownListEditorElement el = ddl.EditorElement
el.PopupClosing -= el_PopupClosing;
el.PopupClosing += el_PopupClosing;
sender, RadPopupClosingEventArgs args)
Point relativeMousePositionInPopup = ((RadDropDownListElement)sender).ListElement.ElementTree.Control.PointToClient(Control.MousePosition);
args.Cancel = ((RadDropDownListElement)sender).ListElement.VScrollBar.ControlBoundingRectangle.Contains(relativeMousePositionInPopup);
If the current version that you use is newer than Q3 2014 (2014.3.1104)
it would be greatly appreciated if you specify the exact steps how to reproduce the problem. Thus, we would be able to investigate the precise case and assist you further.
I hope this information helps. Should you have further questions, I would be glad to help.