On May the 31st I filmed at a place called Sunset Rock by Sparta, TN and experienced some odd behave where the Q500, as I was bringing it in, began to rock side to side so badly I thought it would land on it's side. It then steadied and rose straight up to around 57/60 feet ignoring every input I tried. It hovered there for about 18 seconds before responding to my anxious pulling on the descend lever. It was a hot day with less than 2mph wind, when it did blow, and in view of the location I attributed the behaviour to thermals, after all it was pretty hot and an elevated location. I moved to another location, a cornfield, removed the gimbal and calibrated the accelerometer and the compass. Every flight after that was trouble free. Until that is Sat June 11. Just before dusk I was flying in my backyard, common practice, and on bring it in it again 'went crazy' About 45/50 from me it started gyrating again and began to climb refusing to respond. I had used RTH to bring it back and I believe the acting up began when I switched back to angle mode. Thinking about it, as I have rarely used anything but angle, that was what I may have done back at Sunset Rock. This time it did not stabilize but climbed backwards to around 45/50 ft and around 50 feet from me then simply straight down onto my roof, crashing and sliding down and off the building. The camera and gimbal, which was the one belonging to my third system, separated from the bird and the same damage, as has previously ensued to my first gimbal slide, the horizontal piece on one side broke off. The following day, Sunday 12th (yesterday) I connected it to the GUI and checked the motors and everything the GUI offers, including verifying the ESC allocations. Everything looked good. I took it to a local park and tested it out. It seemed fine initially so I started to bring it back and it went nuts again. Climbing high and out over the lake where it began spinning and descending ignoring all my inputs. It finally sank, the whole system second camera and all, beneath the waters about 190 feet from take off point at a point in the lake I believe to be around 15 ft deep. I had it in mind to purchase another back up and apply for 333 exemption in order to create a service business using the Q500's but am now dubious about moving forward on that until I can understand what brought me to be standing there watching my investment drown.