P2415Q, resizes windows on wakeup

Hi, I have bought a brand new P2415Q monitor, running perfectly with an Nvidia Quadro K2200 at 3480 x 2160 at 60 Hz on Windows 8.1. I am using the mDP port at the monitor and the DP of my graphics adapter. The settings in the Dell monitor menu are correctly set to mDP. However, when the monitor goes into power-saving mode, all open windows are re-sized to a very small size in the top left corner of the screen, which is very annoying. How can I change this behavior?

Thanks.
Ben