FreePBX/Asterisk redials after hangup (ghost in the machine)

I am quite happy with all that Asterisk/FreePBX is able to do, but I’ve run into a problem I can’t figure out.

Sometimes when I call someone through FreePBX, after we’re done speaking and the other person hangs up, about 20 seconds later their phone rings again and nobody is there, it’s like a ghost redial from the server. Again, this doesn’t always happen, and I think it mainly happens if the person I was calling hangs up before I do. Has anyone heard of a similar problem, or maybe have a solution?

Thanks.

Sounds like a NAT issue. Like phones set to NAT when they are not…

Or a misconfig’ed router.

The server is connected directly to internet with no nat configured, and firewall seems to be working OK. Shouldn’t be a router problem, since I’m not using router to connect to internet (using server as router)… although my internal phone is inside my local network… what NAT configuration options could be the problem?