Video card havoc

I’ve been messing around with OpenGL for a bit now and I’ve run into a serious problem. I’m drawing an ortographic scene with depthsorting and lighting off and I draw lots of textured and alphablended quads.
This is all good and fine until I left it running for a bit to test it for stability. To my horror the video card started to glitch after about half an hour. The program didn’t crash and everything ran on as it should except for the fact that all graphics on the system were now distorted (in all other program as well). Luckily it all cleared up after restart.

It seems to me to be some sort of memory leak into the card, but I can’t figure out where it is. The problem dissappeared when I turned off blending, so I guess it has something to do with that.
Now, has anyone else experienced this? Any ideas to what could be causing it? Are there some extra buffers or tests connected to blending that I’ve forgotten about?

I’m on a blue&white G3 with a ATI Rage Pro card.

If I were you I would put together a simple test app that reproduces this behavior and send it off to ATI’s dev support, it may be a driver bug if you’re sure the problem is not in your code.