If i press Ctrl+alt+L to lock the screen, I can get back in by typing my password.
If I put the computer to sleep, wake it back up again, I cannot log in anymore because it says the password is invalid.
The password is valid, because when I press Ctrl+F1 to go to tty1 I can log in using my username and this exact password. Ctrl-F7 back to unity, the same password is invalid, and I have to restart in order to log back in. Very annoying.
The problem is reproducible every time the computer goes to sleep. I have an Intel HD4000 graphic and I'm using opensource drivers. The system is 14.04 with the latest updates through the official channel.