aty128fb stuck in 8-bit

[Peter Abrahamsen <phae@uswest.net>]

Greetings,

  I have a pmac 7600/233 and an AppleVision 1710 AV monitor, using a
"PCI: (0:14:0) ATI Rage 128 RE rev 0, Mem @ 0x84000000/26,
0x80800000/14, I/O @ 0x0400/8" video card. I am running 2.2.15pre19 from
benh's rsync, with only the aty128fb video driver enabled.
  The trouble is that I am stuck in one modeline. If I attempt to change to
a depth other than the default 8-bit, the screen blanks or displays a couple
of mini-images of the screen with strange colors from before I changed
depth.
  My only kernel argument from BootX is video=aty128fb. It's been a bit
since I tried, but iirc the video would do the same thing as if I had
changed the mode after the system had booted when I set a mode on the BootX
line.
  The monitor also occasionally acts as if it were changing modelines (some
flickering on the screen, sometimes a clicking sound) when I change VTs.

Does anyone have any advice, or know what's going on?

Thanks,

Peter