Repoduction steps
Alternative 1
1) Browse to http://demos.telerik.com/aspnet-ajax/input/examples/overview/defaultcs.aspx
2) Click on Phone field -> whole field gets selected
3) Enter 'a' -> One time red flashing border and caret moves 1 position
4) Press 'a' again -> One time red flashing border and caret does not move

Alternative 2
1) Browse to http://demos.telerik.com/aspnet-ajax/input/examples/radmaskedtextbox/firstlook/defaultcs.aspx
2) Click on IP address field -> whole field gets selected
3) Enter 'a' -> Caret moves 1 position, no one time flash of border
4) Press 'a' again -> One time red flashing border and caret does not move

Expected behaviour at step 3 in both cases:
One time red flashing border and caret should be at first position