The guys who came out to the car said they'd never seen it happen before. Probably just a bit of bad luck that the dodgy belt wasnt spotted on the production line, so what would have been a very minor thing in the build turned into a problem for a customer ater manufacture.
This is the only issue i've ever had with a BMW, and i think you can understand 1 in every so many thousand in a batch might have little quality issues.
I'm not worried, if it happens again then that's more of a worry.