Come to think of it, I remember a couple people having problems with CX freewheels BITD. Overall though, they were pretty reliable, and probably comparable to other freewheels of that era. I still have one on my Masi, and never had a problem with it.

Regina Oros were possibly more bulletproof; I don't remember anyone breaking one ever.

I'd guess offhand that it was over-torqued at some point with a removal tool - like gearbasher says, or possibly just a freak break. It happens.