http://ozreport.com/forum/viewtopic.php?t=21387

In looping, the frames needed for fuselage to travel its length is seven to six frames. Seven frames going up and down, and six frames before next pull up, so the speed varies between 88-103 km/h (55-64 mph).

Obviously the speed was pretty high and with Clmax (1.6) in mind, at full pull up the load factor can be easily 6 G's at 88km/h and 8.3 G's at 103km/h. And this is way above 5.3 G's that glider is designed for.

I know, that my calculation is not very accurate, but I am now more convinced that the probability of "pilot error" is more plausible than "design fault".