I've attached a screen grab of what it looks like with the black wallpaper (blank) before I reset it again. Once I set it again, I'm fine until I repeat from a single to dual profile via the docking activity. When I go into the 'Desktop Wallpaper' settings of DF, everything looks proper with the exception of the load image box empty instead of having the path to the image. When I drop the laptop back in the dock and wake it up from it's sleep, the wallpaper transitions from single wallpaper to black.

However, in the reverse, it seems to have trouble. When I snap the laptop out of the dock and then open the laptop, DF quickly realizes the monitor change and displays my single monitor profile. I have 2 monitor profiles (single/dual) with 2 correlated wallpaper profiles (single/dual). I use a Lenovo Thinkpad with one of their Pro snap in docks. Wallpaper Disappears Windows 10 1024x768 Your Desktop wallpaper and the taskbar will disappear when you exit 650x420 Solved Desktop background image.

I believe my issue is predictable but I'm still testing. To add another candidate to your sample, I'm also noticing this behavior and I think it's new as of 8.1.2.

Wallpaper disappears windows 10