Created attachment 41946 [details]
I'm using mainline Linux kernels, and this bug is a regression from 2.6.36. It got broken already in 37-rc series but I haven't noticed it (compiz desktop works fine) and didn't get around to report it in time.
The latest kernel I've tested is 2.6.37-05292-g7bc4a4c running Debian sid.
It appears that the vertical size assumed during display of the mipmap is twice the mipmap's height. See attached screenshot from Celestia which shows the first level mipmap on the central star. Horizontal size seems to be correct.
Zooming outward reveals further mipmap levels with unrelated data as can be seen on the other two stars in the image.
Created attachment 41947 [details]
Created attachment 41948 [details]
DRM specific lines from kernel log
What version of mesa are you using? Does mesa 7.10 or 7.9.1 work any better?
Works here with r600g, reopen if you have same issue with r600g