Start/Stop issue

My partner has a MINI ONE and she has said this has happened twice now. Today the car was stopped on the driveway. Took the foot off the clutch, handbrake on and the engine turned off ie start/stop kicked in. I opened the passenger door to speak to her and then the engine started. She didnt apply the clutch, it just started on its own. She said this also happened at traffic lights last week. Any one else experienced this?