Thanks for setting this up. I just wanted to add my StackOverflow link for reference purposes: http://stackoverflow.com/questions/28769622/canceled-event-is-not-reverting-radtextbox-to-initial-value 

In my implementation, I'm ultimately using the results of an XHR call to set the canceled field of the eventArg. The problem, however, most likely relates to the conditional, aspect of calling radprompt, radwindow, or radalert instances within the encapsulating function.