If you have activated Bluetooth on your WindowsPhone to connect this to another device, then this could result in an issue with the NAVIGON app, which is due to a Microsoft preset function. 

Should the receiving device which is connected to the WindowsPhone offer hands-free or A2DP, then both options will be connected. To deselect one of the options is not possible.

All audio output of the WindowsPhone will be sent via A2DP to the receiving device as soon as the receiving device selects  BT Audio or AUX  as a a source.

The WindowsPhone will always use the A2DP automatically as soon as it is available. We have no influence on this.