I've had that problem before! And for all you who don't believe me or blackbelt, I know how to make it happen again.
Set your screensaver to show the Welcome Screen (in Windows; I don't know 'bout Macs). While you're at it, set it to start real fast (like one minute). Open Toontown and don't move the mouse or press any keys 'til the screensaver starts. When it does, move through the laggy graphics to disable it and get back to Toontown. Ta-dah! One totally messed up screen, extra white.
It happens even with my almost new video card. If Disney would pay attention to things like that, they'd know it's not a laggy video card.