Hi,
I am a bit of a noob with FusionPBX myself, though I have some experience with Asterisk systems (so not a *total* noob with SIP PBX systems, or rather Asterisk/FreePBX specifically). Hopefully i might be able to help you, or at least give you an "a-ha!" moment?
Is the sngrep screenshot from a run on your FusionPBX system or from the system you are calling from? I see the "User-Agent" refers to Asterisk, so I would imagine you ran it from the system you are calling through? What does sngrep show when you run it on your FusionPBX?