Theoretically, this can be desktop animation (or whatever it is called), but XFCE is a very simple desktop manager, and I couldn't find a place where animation is managed. Probably, XFCE doesn't have it.
I would start investigation with something more simple, like basic CtrlLib app and just to count the number of paints.
Maybe even paint that count...
My initial suspection is that this is a part of opening the window, when paint gets called more than absolutly necessary number of times....