FreePBX 2.8 multiple IP routed trunks

I have a very strange issue and I’m hoping someone here can shed some light on it.

I’m running Elastix 2.0 (Asterisk 1.6 and FreePBX 2.7) and I upgraded FreePBX to the latest 2.8 build. (although, this issue was occuring on 2.7 as well so I don’t think that is related, just FYI) I have 2 VOIP carriers trunked into the system. I have a trunk set up using IP routing (NOT registrations). I have also started working with vitelity, which also uses IP routing and NOT registrations. (The service can be set up to use registrations, but with the volume we plan on putting through the system IP routing is the preferred method.)

Here’s the problem… When I installed the Vitelity trunks, oudbound calls work just fine, but inbound calls fail every time. SIP Notify messages are getting to my PBX, but the carrier isn’t getting a response. I spoke to vitelity support and we have been working on this for several days. Finally their engineer suggested that our system may have a problem using 2 different trunks that utilize IP routing. We deleted the trunks and left only the vitelity trunks and calls started coming in just fine. I rely on the trunks for my primary number so we didn’t leave it that way for long, but it told us what we needed to know. For some reason the system isn’t working with 2 IP routed trunks. We changed the vitelity trunk to use registrations and I can receive calls from both just fine.

Does anybody have any ideas? I’m more than willing to post any configuration information that may help diagnose the problem. Any light that we can shed on this issue would be a great help. We really want to get both systems working in tandem. Thanks!