Task Manager undoes overlay?

Ok,I have another weird panel bitmap issue. I recently noticed that, as I test my game with panels that have RGB values of 0,0,0, and the overlay flag set (making the black areas invisible), and open up my Task Manager (I wanted to check memory and CPU usage), that sudenly the black areas became visible, and didn't change back even once the Task Manager was closed.

Anyone have any idea why that might be, and what can be done about it?

Were you running on full screen before you did this?