Sony Ericsson Z600

My Z600 was giving me problems so I sent it in to be RMA'd. SE actually fixed everything but wen I got the phone back, a strange incompatibility seems to have appeared between my phone and my Jabra BT250. When I am on a call and my phone is closed (either initiated via voice dialing or closed after dialing is done) and I have to open the phone again, the mic on the BT250 stops working. I can still hear the person on the phone, but they cannot hear me. The only fix I have found is to manually transfer the sound back to the phone and then back to the headset. I have called SE and they said try another headset. I did (a moto bt headset) and it worked perfectly. I called Jabra and they said it is clearly a phone issue since it started after SE rma'd it. Help...