To reproduce this, use 2 or more instances of a view with RadBusyIndicator in its contents. Then switch the contents of the TransitionControl using the two instances. This brings a slight glitch in the animation. The start width of the animated element gets stretched which should not happen in most animations. 

To work this around, instead of using the RadBusyIndicator as the content of RadTransitionControl, you can wrap the TransitionControl in a BusyIndicator.