Just bought an Asus PA248Q to use for photo editing on a new late 2014 Mac Mini. It arrived tonight. It was connected via short high quality HDMI cable and the Mini had gone to sleep. When I pressed a button to wake the computer up, the monitor woke back up in this state. Obviously a software bug in the monitor. Found one review on Amazon describing the exact same problem. Am waiting to hear back from Asus about a resolution. I'll update if I get one.
Update (from a very long time ago, forgot to update here)
Asus said 'too bad, so sad' after quite a lot of trying to waste my time doing silly things on the mac. There was no fix.