keep in mind carbon fibers themselves have no rigidity, only tensile strength. The rigidity comes from the epoxy and chop mat used in the manufacturing process.

Most commercial CF is epoxy / CF/ epoxy / fiberglas chop / epoxy / CF / epoxy

This layering gives it it's incredible rigidity and strength...picking a poor chop mat will also screw up the part.

I suspect these urban legends might have come from the days when carbon was being first used on bikes and a few less informed makers were using the carbon fiber cloth and epoxy only...no chop...so the components flexed back and forth more easily and eventually had stress failures. In automotive, the early CF applications also had people who tried this with less than fun results. Basically, I really think component makers should say what kind of chop is used...without proper chop, you can't ensure being rigid enough to not suffer from stress fractures in the epoxy.