i just discovered this yesterday. when you connected your bluetooth headset to Z10 the phone locks the volume keys and only the bluetooth device can be used to fast forward, pause and increase/decrease volume.
Confirmed, this appears to be fixed! I was off and on my Bluetooth connection (Ford Sync in a 2011 Fusion) several times yesterday and today after doing the software update and have yet to lose my notifications.
The update is 10.0.10.85. It is my understanding that Bell hasn't released the update yet. I am on Rogers. And the update has done much more than just fix that problem. The other major benefit for me has been the improvement to the battery life.