On a recent road trip, I found I could easily increase navigation instructions volume using voice commands ('increase navigation volume') but every single attempt I made to lower it made it louder! "Decrease navigation volume', 'lower navigation volume', 'reduce navigation volume' - it understood the words but the resultant command was 'increase navigation volume' - it was deafening by the end. I had to go into the settings menu and put it back. Can anyone find a voice command that works?