Serial: CN-OY9PCD-74261-4BQ-0D5L (and another)
Rev: A01 (and another with Rev A00)
Computer/OS: Windows 7 Professional, desktop, Dell Optiplex 9010 MT
Video card: Radeon HD 7850 1GB
Ports: Two miniDP, one HDMI, one DVI
Actual ports used: two miniDP (card) to two DP (monitor). Separate cabels, not daisychained.
Cable used: miniDP to DP that came with monitor, so supplied by Dell.
Resolution: 3840x2160, 60Hz
ISSUE: I use two Dell P2415Q monitors (purchased a few weeks apart, different vendors)--though issue also persists when only one is powered on). Monitors work perfectly at full resolution and speed. When Windows calls for "turn off the display" as part of power save profile, they sleep and wake properly.
When the computer actually sleeps, however, the monitors cannot be woken--striking a key on the keyboard wakes the computer, but causes no monitor response (though audio cues that computer has woken). Cycling the power on the front of the monitor does not help: on return power-on, it indicates that it is responding to the DP port, but then "enters power save mode" immediately as "no computer signal". Actually unplugging the power cord in the back of the monitor, however, causes that monitor to return to function. (The other monitor, if it is on, has to be unplugged and plugged back in separately---restoring one monitor does not restore the other).
Restarting the computer also resets this issue, though (since screens don't work) it can only be done with an undesirable hard reset.
Obviously, a solution would be to never have the computer sleep, or to get used to plugging and unplugging the monitors from the wall. However, this is not desirable. Any suggestions?