Dell e6500 re-enter suspend mode after entering suspend mode on DC and exiting suspend mode on battery

Hi

I'm using Ubuntu Karmic 9.10 64 bits on a dell latitude e6500 (fresh install + updates) (+ compiz enabled)

* uname -a : Linux mydell 2.6.31-16-generic #53-Ubuntu SMP Tue Dec 8 04:02:15 UTC 2009 x86_64 GNU/Linux
* /pvoc/version_signature : Ubuntu 2.6.31-16.53-generic

When I close the lid with the DC power plugged in, the laptop suspends just fine.

If I reopen the lid, it will exit suspend mode and ask for my password (locked session) as expected.

However if I unplug the power cord while in suspend mode and then reopen the lid, it will exit suspend mode and ask for my password *and*, after about 1 second (not long enough to type my password :-p), it will re-enter suspend mode. Then I can resume simply by pressing the power button (it then go back to the password-locked screen and I can unlock)

If the laptop is already on battery when closing the lid, the suspend/resume works fine.

This only happen if I do "on DC + close lid + unplug DC cord + open lid" combination

If I use any other mean (hold power button and select "suspend" option in menu, use suspend button on the keyboard, use top-right corner menu of Gnome --> suspend) to enter suspend mode, this doesn't happen (even if I then add the "close the lid, unplug DC cord and open the lid" after entering suspend mode, it will resume properly)

Reproductible : always
Power manager configuration : I use the default config
Package : ???

In the attachment (dmesg.log), the laptop enters sleep mode at [59884.207720] (=close lid) and at [59894.240039] (=open lid+wake up+sleep again)

PS: except for this bug, suspend/resume/hibernate work perfectly well :-)