version: current git master
The main monitor still has desktop wallpapers & icons as usual.
The second monitor is empty, with a broken background (no wallpaper, only some random window content).
Right click on the second monitor showed the window manager popup menu, not the menu provided by pcmanfm.
So, pcmanfm does not cover the second monitor with its desktop windows.
This did not happen in last release, IIRC, so it seems to be a regression bug.