Workarounds:
(a) Plug your monitor in before logging in; or
(b) Kill and restart nautilus.
Given that the desktop selection rectangle still works while the black/flickering is happening around it, it appears the only thing that's broken is nautilus' wallpaper logic.
Workarounds:
(a) Plug your monitor in before logging in; or
(b) Kill and restart nautilus.
Given that the desktop selection rectangle still works while the black/flickering is happening around it, it appears the only thing that's broken is nautilus' wallpaper logic.