Comment 12 for bug 1320989

Same problem here:

Ubuntu 14.04 64bits, xfce desktop

Intel(R) Core(TM)2 CPU T7200 @ 2.00GHz
Advanced Micro Devices, Inc. [AMD/ATI] RV515/M54 [Mobility Radeon X1400]

Using the drivers from system.

After a long sleep (~1h), unlock the user session and the screen got blank.

I send a Ctrl+Alt+supr and session locks again, but what is curious, is that if I unlock with a different user that has not initiated the session, the session starts and the screen works perfectly fine.

But the original session is impossible to reactivate, it's necessary restart xfce4-session.