STUN setting and Line 2

I wanted to bring this up so that VOIPo knows about it.

My phone service works very well without a STUN server even though I am behind the router. I don't have a STUN server set currently.

A STUN server was set in my provisioning file couple of times during debugging another problem. When the STUN server is set, my Line 1 works without an issue. But my Line2 does not work at all - both incoming and outgoing. If you go to the Devices page, I see Line 1 SIP location with the public IP address and Line 2 has my private IP address. I guess this is the reason why my Line 2 is not working.

Also, noticed in my NAT translation table, that Line 2 (5079 port) has an active connection to all SIP servers (east, west, central, zeus, and one more). My router usually times out the entries after 5 minutes. But these entries do not go away at all. They are open all the time.

Today I saw a DSLreports user also having a similar issue with STUN setting.