It looks like this bug is fixed with current mesa master. Can you please verify
that on your hardware?

-------------------
System information:
Radeon HD 4850
Ubuntu 13.10 x86_64
Linux 3.14
libdrm 2.4.53+git1404110630.504d60
xserver-xorg-video-radeon 7.3.99+git1404022026.ed0cfb
OpenGL renderer string: Gallium 0.4 on AMD RV770
OpenGL core profile version string: 3.3 (Core Profile) Mesa 10.2.0-devel
(git-55f9bbd saucy-oibaf-ppa)
OpenGL core profile shading language version string: 3.30