This is also an issue on my Dell Inspiron 1525, running
2.6.32-25-generic #45-Ubuntu SMP Sat Oct 16 19:48:22 UTC 2010 i686 GNU/Linux
Ubuntu 10.04 LTS - Lucid Lynx
After I type screensaver password the screensaver image still cover the screen. I can Alt-Tab and then see the desktop in the background and activate the different windows. By killing the screensaver I can fix the problem. This happens regularly, but not every time. Often enough to be annoying..
Happens most often after inactivity timer has activated the screensaver.