in former versions of OSM it was possible to stream music via bluetooth to the car’s audio system, while on the same time OSM announced its navigation instructions through the phone’s own speaker, when you set it to use the same channel as system messages. Now, this is no longer possible: the instructions are still streamed to the car’s radio. This is very strange, because normal system messages, like alarms or incoming messages, are not streamed to the car’s sound system.
This does not only stop the music being played unnecessarily, it also results in not hearing any routing instructions at all, if the car radio is set to FM mode with BT being inactive. Only if you turn of BT on the phone you will again hear the instructions.
I have experienced this on two different devices (Samsung and Motorola), running two different versions of LOS (14.1 and 16), using two different cars. The only thing those two devices have in common is the same version of OSM installed, the latest one available in the PlayStore.