Does the restart occur once you press enter. Try pressing enter without typing a password, does it still happen? There is a similar bug here ( https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/874218) which occurs with some artifacting before a restart occurs.
Does the restart occur once you press enter. Try pressing enter without typing a password, does it still happen? There is a similar bug here ( https:/ /bugs.launchpad .net/ubuntu/ +source/ lightdm/ +bug/874218) which occurs with some artifacting before a restart occurs.