The power meters do an auto-reset after about 5 minutes of activity. However if there is any weight on the pedals the calibration is inaccurate leading to reported watts being too high (or too low ?) and issues with extreme left-right balance. This can easily occur if one sits in the saddle clipped in - after a ride looking for other routes/workouts or checking ride stats, etc... and then impacts subsequent rides. (took me a while even with talking to stages support to figure this was what was happening to my strange power figures)
Ideally a longer default (say 15 min? ) or user customizable option would be great!