laptop goes standby after login gnome on battery

I hope anybody can help with my stupid failure.

I installed Karmic-beta (9.10) ubuntu on my laptop SAmsung r-50.
In the standart installation with succesfull configured wpa.

I charge the battery full and start the laptop with both battery and AC are
plugged in. I login into gnome desktop. Until now any problems.

But if i plugged out the battery, after a few time the system goes down without
any warnings.

The failure is that the system goes completly down (hilbernate or suspend, i
don't know), but only the blue-led on the front of the laptop is blinking.

I need to restart. With only AC booting no problems.

The same if i boot with only the (full)battery until "gdm login window" no
problem, but after i login into gnome a few time later (5sec - 1min.) the
system close the screen session and goes standby or hilbernate.

But on kde-desktop i can login and can work with battery without ac.
And on jaunty standard installation, i haven't any problems with battery plugging

During the installation of Ubuntu Karmic i haven't any problems.

Steps to reproduce:
1. Plug the power cable an battery
2. Start the System and login into Gnome
3. work a little bit and plugg out the battery (working until putting out, no
probs)
4. On my laptop few sec. later my screen session is going to close and
goes standby (hilbernate or suspend) because the blue-led is blinking.

The same failure: (starting with only battery)
1. Plug battery
2. Start the System and login into Gnome
3. I can't work a long because after a few seconds Point 4 happends
4. On my laptop the, few sec. later my screen session is going to close and
goes standby (hilbernate or suspend) because the blue-led is blinking

thanks all

I have have the german language configured during Karimc installation, if its importent.