Comment 27 for bug 593226

Since this problem occurred (I don't know when as it's another user who uses gnome and reported the issue to me) I've ran multiple full updates and the problem persisted.

However, I had allowed her to login with no password. Using the System->Administration->Users and Groups dialogue reported that her account was disabled (presumably as it had no password). As root I used passwd to set her account password to a non-null value and then the Users and Groups dialogue reported nothing special about her account (The dialogue always reported that the password was asked at login). On login she was still not asked for a password (as I'd configured pam to require no password, see below) but the problem persisted.

I'd allowed her to login with no password since before GNOME had an option allowing this - I'd put a line in /etc/pam.d/gdm which read

auth sufficient pam_listfile.so item=user sense=allow file=/etc/gdm/nopassusers.txt onerr=fail

(and added her username to /etc/gdm/nopassusers.txt). Commenting out this line meant that gdm asked her for her password and the problem was gone.

Further, I tried un-commenting this line and removing her from nopassusers.txt and the problem stayed fixed. I then created a new user. With the line uncommented: if the new user was in nopassusers.txt problem occurred, if not no problem (even though the user had a properly defined password). the option "Don't ask for password on login" in the Users and Groups dialogue was greyed out for me (as root or not), and searching gave no clues, so I can't test that.

So for me this looks as if it's arising from pam and gdm somewhere.