Ok, solved it!
1) it didn't happen to all users, only me
2) There was apparently more than one place to change resolution.
I use gnome 2.6
From the program menu I had to use Settings->Screen resolution and make the change there, in order
to have 1280x1024.
Bear in mind that I use Swedish as system language, and Settings/screen resolution are my translations.
These entries might be named differently with English settings.