Carbon handlebars hate being overtightened. They (as expected) can easily get crushed and then crack.

A stem that has a sharp edge on the clamping faces will require even less tightening to crush the stem. Bear that in mind if you buy some swanky new carbin bars - it might be a good idea to get a new stem at the same time.

Both completely as the result of mechanics error - I have seen this done on Easton MTB bars and Scud Road bars.

I also ride both bars with confidence on my own rigs.