Comment 7 for bug 874872

I have exactly this same problem, which only started after the upgrade from 10.04 to 10.10

I'm using lightdm v1.0.1

Attaching the lightdm.log found at /var/log/lightdm/
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I have quite a few user accounts set up on my system, so I've tried a few variations on this issue. The problem appears to be linked to administrative accounts.

Case 1:
After booting up:
1. Standard User 'bob' logs in at lightdm login screen.
2. bob selects fast-user switcher, and chooses Standard User 'sarah'
3. Standard User sarah logs in at lightdm login screen.
4. sarah logs out (or just switches back to lightdm)
5. bob logs back in.
6. bob selects fast-user switcher, and chooses Administrator User 'thor'
7. thor types in password at login prompt. Password input screen greys out and thor is not logged in, as expected

Case 2:
After booting up:
1. Administrative User 'thor' logs in at lightdm login screen
2. thor selects fast-user switcher, and chooses Standard User 'sarah'
3. Standard User sarah enters password at lightdm login screen.
4. Password input screen greys out and sarah is not logged in, as expected

I've also noticed that typing in an incorrect password does *not* freeze the password input box. Incorrect password error comes up, and an opportunity to retype the password is provided. Typing the correct password then freezes the box.

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Please let me know how else I might help.
Thanks for your efforts.