[[Special:RandomRootPage/]] returns also from other namespace than main only.
Seems it returns either from content namespaces or 0 + any other even ns >= 100?
On cswikisouirce it returns from ns:0 and ns:100, which are both set as content ns.
It should return only main ns, because it is specified. (unlike [[Special:RandomRootPage]] which also returns ns:0 and ns:100 - assuming the content namespaces.)