I reported the same problem in this thread, including a screen shot. The problem does not persist after reloading a saved game. I'm running at 1920x1200. Display info from my debug.err:
Display Info
Display device 1:
Device Name: \\.\DISPLAY1
Card Name: ATI Mobility Radeon HD 5870
Manufacturer: ATI Technologies Inc.
Chip Type: ATI display adapter (0x68A0)
DAC Type: Internal DAC(400MHz)
Key Device: Enum\PCI\VEN_1002&DEV_68A0&SUBSYS_043A1028&REV_00
Display Memory: 3816 MB
Current Display Mode: 1920 x 1200 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Max Resolution:
Driver Name: atiu9p64 aticfx64 aticfx64 atiu9pag aticfx32 aticfx32 atiumd64 atidxx64 atidxx64 atiumdag atidxx32
Driver Version:
Driver Date:
DirectX Acceleration Enabled: Yes
I only saw the problem after playing the game for about an hour.