Comment 4 for bug 1201405

So after much investigation, this is actually caused by the gsettings-desktop-schemas package. This is the offending commit: http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/saucy/gsettings-desktop-schemas/saucy/revision/46#schemas/org.gnome.desktop.wm.keybindings.gschema.xml.in.in

Notice the changes on lines 63 and 67 where <Super>Page_Up and <Super>Page_Down are added. I think the intent was to support both sets of shortcuts, but Compiz can only handle one, so the first is chosen. Why these new shortcuts are added is not clear to me yet.