There's a crap limitation in tpmgr - it can only handle one factory of any transport type.  This means we can't support listening on two TCP ports.  We've implemented the same workaround in the real PJSIP code to get around this - amazingly it does work because even if you have two listeners on different ports you only need one factory for outgoing connections because the source port is ephemeral on outgoing connections.  (Obviously this assumes one IP address - which obviously works for us right now.)

We're in discussion with Teluu on what the right long-term fix is.