I have tried to fly a few tail heavy planes over the years. They felt like this. After takeoff the plane would start to climb out normally. The plane would then start to roll one way or the other. When I tried to correct with aile the plane did nothing for a split second. Then it snapped in the direction of the aile I was giving. The second one I was able to push it out inverted. After I got rolled back upright I was able to cut the power and kind of glide it down. I say kind of because it did porpoise on the way down. Just a touch of elevator would bring the nose way up.

David