Here's some pix:
It only happens on a few maps. The maps that it's happened to me so far on are: Nuclear Winter, Xenolithic and Altair Crossing. I've been trying to figure what's similar between these maps to find if there's something in them causing it. I haven't been able to think of anything so maybe a mapper would be able to figure it out.
My system specs:
Operating System: Windows 7 Home Premium 64-bit
Processor: AMD Phenom II X4 955 Processor (4 CPUs), ~3.2GHz
Memory: 8192MB RAM
Graphics: ATI Radeon HD 4800 Series - 1920*1200
I just upgraded to the ATI 10.4 Driver to see if it would make any difference, it didn't.