xf86-video-ati 6.9.0 and v-sync

[Nikos Chantziaras]

Trying to enable v-sync (vblank_mode 1) results in this error when 
trying to run glxgears on a Radeon X1950XT PCI-e (r580):

   do_wait: drmWaitVBlank returned -1, IRQs don't seem to be
   working correctly.

glxgears "runs", but with sub-1FPS speed:

   3 frames in 6.0 seconds =  0.500 FPS
   2 frames in 6.0 seconds =  0.333 FPS
   2 frames in 6.0 seconds =  0.333 FPS
   2 frames in 6.0 seconds =  0.333 FPS
   2 frames in 6.0 seconds =  0.333 FPS

also, the kernel complains a lot when switching from X to a VT:

   [drm] Setting GART location based on new memory map
   [drm] Loading R500 Microcode
   [drm] Num pipes: 4
   [drm] writeback test succeeded in 1 usecs
   do_IRQ: 0.83 No irq handler for vector
   do_IRQ: 0.83 No irq handler for vector
   do_IRQ: 0.83 No irq handler for vector

Is this a known bug?

Xorg.0.log: http://realnc.pastebin.com/m28ee9247

System:
AMD64 (Intel Core 2 Duo)
Linux kernel 2.6.26
xf86-video-ati 6.9.0
xorg 1.4.99.905
mesa 7.1_rc3
libdrm 2.3.1
xf86driproto 2.0.4