That's not a bug.
If the car is awake (and there's a correctly set up USB storage device attached) then teslacam is recording. Period. Park, drive, doesn't matter. Car awake=recording.
All sentry does in this regard is keep the car awake the entire time it's on... (and if it goes to alert, move the last 10 minutes of teslacam footage to the sentry folder and do the light flashing/screen display thing).
With sentry off teslacam will record for a while in your garage anyway until the car goes to sleep normally.