Andrew,
Although 3476 hasn't broken a belt this season it has been something that we were very careful to design against at the beginning of the season and something that we are very eager to prevent from happening.
That being said, could you tell us of 256's setup and what was this expected "fluke" that could have caused your failures? We sourced our belts from VEX this year and we have been quite happy with them so far. Seeing this is our first year using belts we are still learning.
Thanks!