Rukla

We did not know about any bubbles in the prop structure. When the airplane was ready to fly, we took the most adequate prop for the ZG20 engine. From our experience, we also know that 2 blade prop has better performance and has lower drag, but 3-blade prop is a better choice for scale models, such as Yak54. We do not fly 3D program and are not interested in 3D figures.
We have over 15 different airplanes (warbirds, biplane, aerobatic, etc) and use 2-blade and 3-blade MAS props and so far we had no problems.
To make the story short, the only problem is that we contacted first the manufacturer with the idea of alerting him about the problem. The lucky fact here is that the prop broke in mid-air - had it break on the ground, just imagine what would happen with the model surrounded by people.
The manufacturer responded very unprofessionaly. He even did not offer any replacement for the broken prop.
In one of the previous posts, there was a mention about RPMs over 11000 - it is impossible.
Resume:
Imagine the comments if my friend Robi did not shot a video of the flight?

There is evidently a material flaw, the engine which looses a prop blade in flight, breakes the firewall and the rest of the airplane nose, due to disbalance. In our case, there was also a engine damage - bended crankshaft.

It would be logical that the manufacturer of the prop compensates the damages. His answer was that he would only compensate for the shipping of the broken prop and DVD recording.[:-]