I tried running the 6.8.2.dfsg.1-7 server, and was unable to reproduce this bug using your configuration file only changing the busID. Have you tried the latest xserver-xorg to see if you are still able to reproduce this bug?
here's my output of lspci -v
0000:01:05.0 VGA compatible controller: ATI Technologies Inc RV280
[Radeon 9200 SE] (rev 01) (pro
g-if 00 [VGA])
Subsystem: VISIONTEK: Unknown device 7c13
Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 201
Memory at f0000000 (32-bit, prefetchable) [size=128M]
I/O ports at d800 [size=256]
Memory at df000000 (32-bit, non-prefetchable) [size=64K]
Expansion ROM at effe0000 [disabled] [size=128K]
Capabilities: [58] AGP version 2.0
Capabilities: [50] Power Management version 2
0000:01:05.1 Display controller: ATI Technologies Inc RV280 [Radeon 9200
SE] (Secondary) (rev 01)
Subsystem: VISIONTEK: Unknown device 7c12
Flags: bus master, 66MHz, medium devsel, latency 64
Memory at e0000000 (32-bit, prefetchable) [size=128M]
Memory at de800000 (32-bit, non-prefetchable) [size=64K]
Capabilities: [50] Power Management version 2
-stew
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