I am not sure this is a gnome-power-manager issue by itself. I experience this same issue using an ATI Radeon 8500 video card in Ubuntu 10.04. Unfortunately, I can test it in Ubuntu 10.10, maverick, because it shuts my video, keyboard, mouse off before I can get the grub menu. Changing to an Nvidia 6200 video card resolves the issue completely for me.
I am not sure this is a gnome-power-manager issue by itself. I experience this same issue using an ATI Radeon 8500 video card in Ubuntu 10.04. Unfortunately, I can test it in Ubuntu 10.10, maverick, because it shuts my video, keyboard, mouse off before I can get the grub menu. Changing to an Nvidia 6200 video card resolves the issue completely for me.