

I don’t use pacmanfm but it seems like it is rendering wallpapers itself, so using both is not the way to go.
Instead you should try to set the wallpaper in pacmanfm. A short search brought up the following command but I did not test it:
pcmanfm-qt --set-wallpaper=FILE --wallpaper-mode=MODE
This I really like Debian but on my everyday “production” system I run LMDE. I still have Debian in all it’s glory but also all those small extra convince features and we’ll thought out defaults.