That would be an engine fault lol. I dont think any amount of thrashing would do that. I should think there was a crack in the crank shaft. As they dont crack test them at the factory afaik. A crack in a shaft is dangerous due to the high torsional loadings on it, so it would fail quite easily. (i would go into the maths but i cant be ar$ed).

Sounds like a manufacturing fault, just hope the hobby shop understands...

Cheers,
David