SOLVED Background images on multiple displays changing randomly

[topsoftbe]

I have installed Win 10 from scratch (no update). I have 3 monitors. I have created a theme with a different background image on each monitor. After a random time, the three images are suddenly mixed up, image 1 appears on monitor 2 or three, etc. When I click on another theme and then on my own theme, the images are restored to the correct monitor.
My PC is part of a domain. Some buttons on the themes page that I had in win 8.1 are now gone, so I am unable to select things like slideshow etc. In fact, beneath the window with the themes, I have no buttons at all.
Does anyone know if there are some settings in the registry that I can use in order to prohibit the changing of the backgrounds?
I tried Group Policy but that didn't work out.
Any help would be appreciated.

 

[topsoftbe]

Found it myself. It's hidden deep down where you would never expect it. Control panel/Power options/Change plan settings/Change advanced power settings/change settings that are currently unavailable/ Desktop Background settings/Slide Show/...
set everything here to paused (battery and grid)
One could at least expect to have a simple button where it belongs: under "Themes".
It's another example that proves that windows 10 is not more than some kind of beta. The underlying framework may be a little bit better than win 7, but the user interface is a real disaster. On the one hand you have those disgusting big squares, on the other hand you have to work your way through xp-style menu's. The squares are a disaster on a pc while the old style interface is unusable on a phone or tablet. Luckily we have Classic Shell.
Anyway, thanks everybody for the great help.