So the past few flights I've noticed that it has not been particularly stable in GPS mode (ie drifts around a lot) even when I have full GPS lock (no red flashes). Today I was letting someone else fly it in ATTI mode, and it went out a fair distance. I took over and switched it to GPS mode to try and bring it back in, and it started behaving really oddly. eg. pushing the right stick suddenly made it start diving at an angle -- this should never happen since I wasn't even touching the left stick! I was sure I was going to lose it, but I finally somehow managed to bring it back to my location (in GPS mode). It was directly above me about 30 feet up and in a stable holding pattern. I pulled down on the left joystick to lower it and it wouldn't budge... even when I pulled the stick all the way down. I switched to ATTI mode and it came down normally. So something is clearly borked in GPS mode. Now I'm scared to fly it at all in GPS mode or try failsafe/GTH. Any thoughts? Can the GPS become uncalibrated? I checked the IMU calibration immediately prior to flight and it was perfect.