I have a Dell XPS 13 (2015) hooked up to an Asus 23" (MX239) monitor. They are connected via DisplayPort to HDMI cable. Both displays are set to 1920 x 1080px (their native resolution). The Dell XPS display is set to scale otherwise everything would be tiny. Also, for more detail, the Asus monitor is my primary (#1) display, and the Dell is display #2.
The big and super frustrating problem is that very frequently when the screens gets turned off by the Windows "Power & sleep" settings, all my windows on the Dell XPS 13 get moved over to the Asus monitor, as well windowed problems that are not full screen have their position on the display altered. Again, this happens when the displays are turned off by Windows, this is before the computer goes to sleep. When I touch a key or whatnot to wake the displays, they turn on and I see the above issue of moved and resized windows.
I am aware of this thread, which is still active, but it is titled Windows 7, and I noticed a Microsoft employee 4 years ago suggested starting a new thread. Since we are now through Windows 8, and on to Win 10, and this is still happening to people, let's start fresh here and get this fixed! Please. Please. Please.
I have also tried the reg edits some folks suggested in that old thread with no luck. And in my research it really does seem this issue is more common with folks not using HDMI to HDMI to connect their displays.