HiddenServicePort TARGET IPv6 address
The man page HiddenServicePort does not say anything about TARGET being an IPv6 address. Since Tor is becoming IPv6 enabled it probably should (ie: ::1, and precedence). There are some combinations to consider supporting if not already done (latter dependant on host if tor is not bound to both)...
4 -> TARGET 4 6 -> TARGET 6
4 -> TARGET 6 6 -> TARGET 4