Thansk senorcat - it worked as a workaround for me as well. The voice navigation now comes out of my phone speakers. The funny thing is that when I'm in a call the voice navigation now comes out of the car speakers :-) Weird!
I have the exact same problem with my HTC One paired via Bluetooth with a Parrot MKI9200. No problems with music or telephone calls but voice navigation doesn't come through. :(