What you describe is similar to an aerobatic "bunt" maneuver, Jeff. There can be a lot of necessary downward force created by the horizontal control surfaces , especially when holding the nose high to perform something like a power on stall, for instance. If that tail gets into some disturbed air, like from the flaps, at a particular angle of attack, it can result in a tail stall, instantly loosing all of that down force. A forward CG can be one of the contributing factors to something like this as well. The result can be spectacular... I experienced it once also, in another aircraft type, and it was a wild ride for a guy who didn't know exactly what was going on. Even though the nose went beyond vertical, and I was hanging from the shoulder harness, the tail remained in disturbed air and stalled until I retracted the flaps, and had lost about 7,000 ft., pulling out less than 500 ft. AGL. My first thoughts were that something had broken in the elevator control system. If I hadn't had mechanical flaps, with the flap lever sticking up to remind me that they were deployed, I would have ridden it into the ground. It was a fast, slick little airplane, on it's second test flight, and even if I had figured out what was happening a few seconds sooner, electric flaps may not have retracted soon enough. Anyway, I think it's important to share your experience like you did. I'm glad you got out of it in time. I don't think it will keep me from trying the spring assist. My belief is that the test flights of a new airplane, performed at altitude, are very important for discovering any adverse traits and the conditions under which they can occur. I'll make sure that I'm looking for that when I'm testing mine. Thank you for letting others know.