Then I'd suspect that it has something to do with the carrier.
Turn on "replace CLID" in the PRI circ descriptor and retest.
You could also test with the polycom by making both calls from it. That assumes that one leg of the call in incoming.
I'd bet that would work.
You can also test using any other phone. I'd bet it's system wide. (Incoming call, then place LD call)
Ralph