Bluetooth & 'Call Transfer'

In this thread, I'm recapping how to switch a Bluetooth-connected conversation from the JBL audio system to the handset, followed by a question in regards to that.

When you have the JBL Bluetooth function for your car and you pair it up, you can make and receive phone calls over the JBL system. If you want to have privacy, you can go to your handset and select "Active Handset" (or something similar) (credit: found this answer in another thread here) or push the car's Talk button and say "Call Transfer" (I think I got this from the manual.)

I have a Blackberry Pearl, and here's the question for this thread:

When you activate the handset or provide a "Call Transfer" voice command, the conversation switches from the JBL system to your handset. I've noticed that after talking for a few minutes (perhaps 5 minutes?), it automatically switches back to the JBL system. That's annoying. I'd rather have the conversation STAY with the handset until I hang up.

Has anybody notice that happening too? If yes, what's the workaround for it besides disabling Bluetooth pairing with the car?

Another possibility is that the Blackberry Pearl is causing this -- meaning, this may not happen with other Bluetooth phones.

Michael