As a workaround, it seems as though manually copying schemas in to /usr/lib/monodevelop/AddIns/MonoDevelop.XmlEditor/schemas/ and then restarting MonoDevelop works.
As a workaround, it seems as though manually copying schemas in to /usr/lib/ monodevelop/ AddIns/ MonoDevelop. XmlEditor/ schemas/ and then restarting MonoDevelop works.