Just went outside for a two minute test… at 40 seconds I unclipped left shoe and pedaled with only right foot as seen here in Garmin Connect:
^ that was recorded on Garmin Edge 530
Now lets see what TrainerRoad app on iPhone recorded… I pressed record on Garmin at same time as starting TrainerRoad… and TR has 5 second countdown and so its 5 seconds behind:
Both are showing 116W at the same time, and there is no power being applied to left pedal.
Conclusion: TrainerRoad is receiving power from right side via the Stages left crank power meter, over Bluetooth, and not simply doubling as stated in that post above.
@Bryce can you please comment on that?