It results in massive amounts of this printout:
radeon: The kernel rejected CS, see dmesg for more information.

dmesg says:
[  824.623357] radeon 0000:01:00.0: evergreen_surface_check_2d:285 cb height
1088 invalid must be aligned with 128
[  824.623362] radeon 0000:01:00.0: evergreen_cs_track_validate_cb:427 cb[0]
invalid (0x000000df 0x000076ff 0x00090c80 0x01088468)
[  824.623364] radeon 0000:01:00.0: evergreen_packet3_check:2136 invalid cmd
stream 607
[  824.623365] [drm:radeon_cs_ib_chunk] *ERROR* Invalid command stream !


I've got the kernel from vanilla source, and mesa from package (debian
unstable). Mesa 9.1-dev works fine. I've got libdrm 2.4.40+ from git
(0980633afd9c7eecc0c75ef3bea4d3c6b7aa1898) installed in /usr/local/lib.