weird suspend/resume shutdown problem with Ubuntu 10.04/Dell D530 laptop

[bogstad-e+AXbWqSrlAAvxtiuMwx3w at public.gmane.org (Bill Bogstad)]

I have a Dell laptop (D530) which is currently running the 64-bit
version of Ubuntu 10.04.   I have setup gnome-power-preferences so
that when the lid is closed (and the AC adapter is connected) that the
machine will go to suspend mode.    On battery, it is supposed to
suspend and shutdown when the battery level is critical.   The problem
is that when on AC it only wakes up successfully if I don't wait too
long.   If I leave the lid closed too long, when I open it up again it
shuts itself down.   I can't say exactly how long it takes, but it has
to be suspended for at least 2-4 hours for this to happen and it
always happens if I leave it suspended over night.  Oh, the battery is
at 100% when I immediately reboot it, so I don't think this has
anything to do with the critical battery level shutdown setting.

Any ideas?

Thanks,
Bill Bogstad

P.S. This happened with Ubuntu 9.04 and 9.10 as well...