To recreate, try these steps:
- Boot up the machine (it happened on a cold boot, so I haven't tested on a hot boot yet)
On the login screen, type in your username
Without typing in your password, click on the power icon
Proceed to enter your password and click OK
Again nothing happens
I'm using Linux Mint 15 MATE 64-bit with MDM 1.2.5+olivia. I was using the default "clouds" theme.
EDIT: I easily recreated the unresponsive power icon, but it still logged in afterward, so I have yet to recreate the second half of this. This was also on a hot boot and not a cold boot, as well.
EDIT #2: This same issue did not occur when I tested it with a 32-bit Linux Mint 15 Xfce VM I have.