When a user locks the screen and another user tries to enter, the system first paints the white space for the password textbox, but doesn't put the cursor in it. Afterwards, no textbox appears, so the first user cannot enter the system neither.
System shutdown or restart doesn't seem to work neither, so the only option is a hard reboot (maintain the power button pushed until the computer powers down).
The question is if there is a way to prevent this from happening (without having to logout every time)?
Just filed a bug report in Launchpad.