This has been bothering me for too long that I decided to make a video to point out this "problem". I would assume that the FSX2ANDROID forwards NMEA message for HDG (heading) as TRK (course, track) information into the Fly is Fun app. This could be the reason for the "weird" behavior.
Also, I would like to request a new feature: Increase data update from 1Hz to atmost 10Hz.
Warning: I might have recorded the audio a little bit loud.