Hi,
I have a limited experience which is similar to yours.

A friend of mine (another 30+ year modeler and pilot) bought one of these about a year ago and I put a test flight on it. It was equipped with a Moki 1.8. The controls were set up for non-3d travels and I didn't watch the CG being checked on the bench, but he demonstrated a ball park check in the field that I did witness. The airplane had a wing waggle on climbout , but otherwise flew pattern type maneuvers very well.
I ended up with a flame out at altitude, inverted at 1/2 throttle and simply needed to make a 180 degree turn while the airspeed was up. No big deal right.... I didn't even pull aggressively and the airplane snapped. I immediately gave up the back pressure I was holding and even more gently concentrated on recovering level without a secondary stall. It snapped a different direction 3 times (total) and I managed to pancake the airplane with wings level and level flight attitude and the only damage apparent was a monokote tear and sprawled landing gear. Needless to say, it was sheer luck that I hit wings level. (or was it) The airplane was repaired to fly another day and on landing the wing collapsed downward.
I wasn't there to witness that, but the airplane needs a new wing. I had heard that the early runs of these airplanes had a wing structural problem. I've been flying and test flying all types of models for years (30+) and I've read alot of good about this airplane, but this was the worst tip stalling airplane that I have ever flown.
I can only believe that the set up, or the wing was the discrepancy. I would check both and pay alot of attention to: CG (check at the root near the fuselage), control travels, wing warp, and a washout check.... ) maybe you've done this thoroughly already and are satisfied....

Hope this helps....
Chris