Ubuntu – Wallpaper suddenly went black on Ubuntu 13.10

This one is really strange. Two days ago the wallpaper on Ubuntu 13.10 simply went black. I have repeatedly tried to change it in the Appearance menu back to an image, or one of the default wallpapers, but it remains persistently black. I have no clue of what to do. Thanks.

Update I: some things I have tried that did not work:

• gsettings set org.gnome.settings-daemon.plugins.background active true

• Purging the gnome3 PPA

• Setting the wallpaper with Firefox

I have desktop icons, thus I don't think that could be a cause.

Update II: I captured a video of this strange desktop behaviour.

Update III: other fixes that are reported to work on Ubuntu 13.04, but are unsuccessful on Ubuntu 13.10:

• Resetting configurations

• Unticking the "show desktop icons" option (it doesn't exist in Ubuntu 13.10)

• Unticking "Have file manager handle the desktop" in Gnome Tweak Tool

• Changing the GTK theme to Adwaita

Update IV: Logging in to a Gnome Flashback session I get the same behaviour with the wallpaper.