I also discovered that if I push the hinged front trigger forward and let it snap back into position quickly, it trip the sear on that side. Maybe that's why it doubles? Maybe my trigger finger makes contact with the front trigger and recoil and allows it to come back quick enough to trip the sear. I can't detect my finger actually making this contact though, although it could be. I should try and film myself and see what happens when I fire it. Probably need a high speed camera though - these can be hired.