Probably since the first time I used 50.cab (or even earlier)

I've had this small bug. The screen flashes something that looks like a window border around its edges for about 1/4 of a second probably every 15 or so minutes. Might be just my box's fault.
I'm running WinXP Prof., 1.2Ghz, 256DDR. Zdoom runs in fullscreen, 640x480.