I learned a lesson today. I was out flying in strong winds, and after spending the first 2 batteries on playing with the wind, I decided to use the third battery to do a Ground Station run. My plan was to use two large sports ovals, separated by a few 80 ft trees. I set a couple of points at 33 ft, in the oval that I was standing in. Then I set up a climb to 120 ft for it to go over the trees to the second oval. A couple of way-points later I had it set to return to my oval and descend back down to about 40 ft. A couple of more way-points and it would be over the home point. Great plan. While it was executing, I decided to grab the camera and take some pictures. As my Phantom crossed back over the trees towards me, it abruptly deviated from the plan and looked like it was heading for the first way-point again, thankfully all above tree height. Wide-eyed I watched as it continued to fly away from me. I put down the camera and grabbed the controller, ready to flick S1 and take back control, which is what I did, but I found it already at 2nd position. Somehow I had knocked the switch out of GPS mode and into Atti mode, which sent my Phantom drifting at speed with the strong wind. Note to self: Stay with the controls and have someone else take the photos.