Debranded z310 Bluetooth Issues

Hey all, I have a debranded z310 running firmware R8BA024.

The phone has been working perfectly fine, but I just recently got a bluetooth-enabled GPS that has handsfree support. It works great with my w300 but the z310 is not playing well at all...

The phone goes totally mental after it has been connected and then disconnected again - it gets stuck in kind of a half-way handsfree mode where the speaker built in to the phone is active but there's no way to turn it off. To get back to "normal" phone mode I have to power the phone off and on.

Any thoughts? Is there a different firmware I should consider trying?

Thanks!!