Please describe the problem:
In the new gdm you need to press alt+_key to get to the language/keyboard/session selections since tab doesn't bring you there if you wan't to change them by using your keyboard. But once you do that, it's impossible to input a password since the password input field cannot be reactivated neither by keyboard nor by mouse.

Steps to reproduce:
1. select your username
2. switch to the bottom bar by pressing alt+s for example
3. try to input a password


Actual results:
It's impossible to reactivate the password input field so you can't input a password, just cancel or try to log in without a password which doesn't work.

Expected results:
You can input the password.

Does this happen every time?
Yes.

Other information:
Was originally filed as https://bugs.launchpad.net/ubuntu/+source/gdm/+bug/405006