gnome session defect after "Automatically save changes to session"

Problem:
My gnome (session) is defect since I enabled the "Automaticaly save changes to session" setting in the gnome-session-properties. When I logged out the last time, some windows were open on multiple workspaces. On the next login, gnome got unuseable:
I don't have any window title bars anymore,
the windows are not shown in the window list of the gnome-panel and
all windows Stick to the upper left corner and I can't move them...
And lots of other strange problems.

Do you know what I can do to reset my gnome session to a useable state?

I have tried:
to apt-get --reinstall install gdm, gnome-session, ...
the same with dpkg-reconfigure
to fix it with the gnome-session-properties applet (Save current session...)

Thanks for your help!