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.

To work this around you can set the EnableColumnGroupsVirtualization to False.

Alternatively you can change the FrozenColumnCount before adding the columns, and reset it once the process is done. For example:

gridTriffDetails.FrozenColumnCount = 0;
 
gridTriffDetails.Columns.Add(newColumn);
gridTriffDetails.Columns.Add(newColumn1);
gridTriffDetails.Columns.Add(newColumn2);
 
gridTriffDetails.FrozenColumnCount = 1;

Currently the new item's properties are validated before editing their values, which is not intuitive, especially for Required, MinLength etc. The correct behavior would suggest that validation should be applied only to "confirmed" property values.

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.

Not all of the FilteringControl elements have automation IDs. This fact prevents the proper usage of some automation frameworks.

Workaround: reused the cell element like this:
CreateCellElement(Telerik.Windows.Controls.GridView.GridViewCell cell, object dataItem)
{
    var button = cell.Content as Button;
    . . .
 
    return button;
}