I'm not exactly using Ubuntu (but debian), and gnome 3.14, and I had a lot of problems with disabling desktop handling by nautilus. Gconf entries were missing and Tweak tool didn't have "Have file manager handle the desktop" option. And option labeled: "show desktop icons" didn't work.
In gnome3 by default nautilus is not handling desktop, so if you nuke your gnome3 config it'll revert to defaults and desired behaviour. If you are using xfce or other desktop enviorment there's fair chance you wont miss these settings.
Instructions on how to delete (or backup!) them are here: How do I reset GNOME to the defaults?, or just execute this will erase all gnome3 configuration:
rm -rf .gnome .gnome2 .gconf .gconfd .metacity .cache .dbus .dmrc .mission-control .thumbnails ~/.config/dconf/user ~.compiz*