WTF?
looks like your GPU is f*** up.
Please try to use
Threads[
^].
That might be an issue of the GUI Thread hanging because you messed up something at another corner. Therefor the GUI is not redrawn correctly.
You can add a Thread to your Dialog factory (if you have one or at least a centralized point to launch the Dialogs).
But I guess you have a far bigger problem - something ruins your GUI Thread... How is the RAM load? Does the application run into a heap space? I bet so.