Although I only got 1.5 hrs on the Puma, and never did experience the roll/yaw divergence, one of my mates did on his ETPS preview, with an experienced Puma QHI. It happened when they rolled into a turn and added some pedal to keep the ball in the middle - surprised them all.
Evidently it only happens with a rear CG- lots of surface area ahead of / above the CG, and the pedal input added the necessary sideslip to cause the machine to roll pretty smartly.
That's why the later versions have the added area at the fin at the back.