I'm using xorg-server 1.9.2, Mesa 7.9 git (20101027) and xf86-video-ati 6.13.99 git (20101029).
VirtualBox always worked fine with my integrated RS690 X1200, but with the recently acquired 5450, it crashes as soon or a few seconds after I change/return to/from seamless or fullscreen mode. I used 3.2.10.
I captured the attached backtrace compiling the three packages with -O0 -g3.
I'm also attaching my X.org.log.
Created attachment 39962 [details]
Created attachment 39963 [details]
X session log
*** This bug has been marked as a duplicate of bug 30754 ***