I just purchased the ASUS PB287Q (4k @ 60Hz) and I am running into the same issue. I am only using this one monitor for now and unfortunately I HAVE to run this with Displayport 1.2 to get the 60Hz @ 4K resolution.

I'm running windows 7 Ultimate and have a NVIDIA GeForce GTX 750 Ti.

After my research, some monitors don't keep the ports "alive" when they are powered down.

As a result, when windows reboots or comes out of sleep, it can't detect a monitor, so it sets resolution to it's "SIMULATED" monitor registry entry in the key at;
HKLM\SYSTEM\CurrentControlSet\Control\GraphicsDrivers\Configuration

This can be manually edited to contain the actual screen registration of your default monitor.

Discussion: http://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/windows-7-movesresizes-windows-on-monitor-power/1653aafb-848b-464a-8c69-1a68fbd106aa