Was it flying OK before you upgraded the firm ware ?
Yes. I had it only couple of weeks and flew only few times before upgrade and no problems. And no problems after reinstalling upgrade.
I just tested it after snow fall. The drone switch off if on the ground when turning RTH on. Then I tried taking it up about half a meter and flew it 2-3 meters away and turned RTH on to see if it kills motors during flight. RTH worked as it should be, the drone went up to 10m and then descended to starting point. And I was closer to the drone (4-5m) than when the accident happened (8-9m). So it looks even more than there was some problem with upgrade.