+The desktop-theme-growing package manually sets your Gnome3 wallpaper
+by a script that runs everytime you login to Gnome.
+This script is located here:
+It sets the wallpaper to the alternative "desktop-background".
+If you want to use a custom wallpaper, you might want to
+- uninstall the desktop-theme-growing package or
+- delete the script /etc/xdg/autostart/growing-autostart.desktop or
+- use update-alternatives to link the alternative "desktop-background"