A workaround for the issue is to use RadObservableCollection as a source collection. Before the items are added to it, call the its SuspendNotifications method. Respectively, after that call the ResumeNotifications one. 

Another approach would be to populate the items through the AddRange method of the collection.

1.   Run the sample application.

2.   Scroll to the last item.

3.   Begin to resize the window. The direction is irrelevant. Only the horizontal scrollbar needs to be visible.

4.   Observe that in the beginning of the resizing, the scrollbar auto scrolls upwards a little and the last item is half hidden.

A kind of a workaround for the user: resize any column/the entire window or collapse the row details.

The issue seems to be a bug with UI Row Virtualization since once I set it to False, it did not occur any more. You can also refer to the documentation on UI Virtualization: http://docs.telerik.com/devtools/wpf/controls/radgridview/features/ui-virtualization.html