12.04 crashing on display shutdown

[Colin Law]

I have 12.04 Alpha installed and have a consistent crash if I have the
display set to power down on inactivity.  It seems to be a complete
system lockup with no response to anything including ctrl-alt-f1 and
ssh access.  I can't see anything in any of the logs but it is
definitely to do with the display power down, it runs happily all day
if the display is set to never power down yet always crashes if set to
power down.

Can someone suggest which package I should report a bug against?

Thanks

Colin