I know exactly what I'm talking about. First of all, I'm not talking about Solitaire or "Hold'em Texas" (whatever that is), I'm talking about the XP graphics bug where everything locks up when you're copying files remotely and you can fill your screen with window shells. Actually, XP often likes to lock up entirely while it's busy copying files. Can't seem to handle the multitasking thing sometimes.
Happens on my brand new laptop, happened on the laptop before it, and the one before that.
It's not a bug. It's documented in about every Windows programming book there is and it has been consistent behavior since the early Win16 days. In Win32, which every other Windows framework is derived from, WM_PAINT messages are queued as low priority in your apps message queue. Most messages will override it, including all input and I/O.
So if your app is busy writing to the network, it's not redrawing its window. If you drag another window partially on top of your app that is busy writing stuff out and drag it away again, it will leave a blank square and the OS will queue a WM_PAINT message with the RECT structure that needs updating. This can sit quite a while in the message queue until your app gets to it in its main loop.