I do this fairly often as a backup especially when double checking courses/controls (you can do it with Check Site as well). I would not say it is being fooled as it is actually running two "separate" events at the same time. This also means that you will end up with two different event results so I would suggest you turn off automatic uploads so you can use your watch for the results, but, if a problem with the MapRunG results occur, you can upload the phone results (or other way around). Assuming no issues with GPS, I generally get a punch at a very similar (not not exactly) time on both the watch and phone. I do not however generally use the map on the phone unless doing a Check Site and something is wrong. Also realized that, with MapRunG, if Garmin Connect on the phone is set up for audio laps, you get the audio lap indication from the phone each punch (lap) although the corresponding number is out (S1 punch is lap 1 so control 1 is lap 2 - still handy incase you don't see/feel the watch indicator).