I have an ASUS PA328Q 4K monitor plugged onto the DisplayPort output of an MSI NVIDIA GeForce GTX 970 4G. The monitor is configured to use DisplayPort 1.2. I am running Windows 8.1 Pro 64-bit. The monitor works fine at full resolution (3840x2160 at 60 Hz in RGB mode).
I however suffer from the classic Windows+DisplayPort issue where Windows resets the position of all open windows to fit in a 1024x768 top-left rectangle whenever the monitor goes to sleep or is turned off (either manually or by Windows itself). This issue is well-known and well-documented, including here on Super User: 1 2
There is a registry trick that essentially allows to specify the resolution Windows should default to when no monitor is plugged. It does have an effect, and appears to be enough for most users.
Unfortunately, this trick is not sufficient with the PA328Q monitor. By connecting to my computer from another one via TeamViewer, it appears that the monitor first switches to 2560x1600 for a split second before switching to full 3840x2160. This is enough to cause Windows to resize all windows to fit into a 2560x1600 rectangle.
ASUS tech support refuses to provide any support unless I first follow their "helpful instruction" to reinstall Windows.
After weeks of investigation, I am desperate for any solution that doesn't involve a shoddy program recording each and every windows move/resize actions in order to restore windows later.
EDIT: A detail that eluded me until now: during the brief instant where the display is in 2560x1600, the NVIDIA control panel reports that the monitor is connected through DVI (which it isn't, of course), and 2560x1600 appears to be the maximum resolution supported by DVI.