"snow" when turning down brightness

[Tamas K Papp <tpapp@Princeton.EDU>]

This is really weird, it is the first time I see this.  I keep turning
the brightness down with pbbutoonsd, and are at the point where it
should go blank.  But it does not!  I get this:

http://www.princeton.edu/~tpapp/snow.jpg

http://www.princeton.edu/~tpapp/snow.avi

(the latters shows this shot with my digital camera, going from lowest
level to snow [should blank], then up [black screen] then up [lowest
brightness]).  As the movie shows, the "snow" starts spreading from
the upper left corner and actually moves.  Really weird.  Is this a
kernel bug?

% lspci
0000:00:0b.0 Host bridge: Apple Computer Inc. UniNorth 2 AGP
0000:00:10.0 VGA compatible controller: ATI Technologies Inc RV350 [Mobility Radeon 9600 M10]

% cat /proc/cpuinfo
processor       : 0
cpu             : 7447A, altivec supported
clock           : 666MHz
revision        : 1.1 (pvr 8003 0101)
bogomips        : 663.55
machine         : PowerBook5,4
motherboard     : PowerBook5,4 MacRISC3 Power Macintosh
detected as     : 287 (PowerBook G4 15")
pmac flags      : 0000001b
L2 cache        : 512K unified
memory          : 512MB
pmac-generation : NewWorld

Thanks,

Tamas

PS.: Mplayer does not play the video on my machine, but
totem-gstreamer does.