Multi audio tasking is not working correctly if a Zumo 390 is paired with the 20S as "GPS"

The phone is connected to a Zumo 390. Zumo is connected to 20S as "GPS" device.

Phone functions are select-able, also answering a call. But the MIC is not open so they can't here me.

Connecting the Zumo as "Phone" will disable the multi audio function. Every GPS instruction will close the intercom shortly.