No login screen when using dual screen configuration and themed login screen

[Philippe]

Gutsy RC, clean install, NVidia 6800 GT with restricted drivers. All packages up to date (Extra Visual Effects working perfectly with single or dual screen configuration)
When in single screen configuration everything works perfectly.
When activating the second screen and exiting the session, I see activation of the two screens (nVidia logo displayed). Then login screen wants to start but instead I receive the following message: 'Le programme de la bannière d'accueil semble être défaillant. Tentative d'en utiliser un autre" (Welcome screen program seems to be defective. Trying to use another one). I have to click on validate then the same problems occurs.
When I go to a console and change the xorg.conf to a single screen config, everything goes back normally.
From the single screen configuration, using the Systems --> Administration --> Login screen configuration tool, I change this login screen to "simple" and set the xorg.conf back to dual screen. When I log off, everything works well, I see the correct login screen.
From this working configuration, I change back to "Human", "Human List" or "Circle" theme, same problem occurs.