afaik it is not common. I've had a dozen of these now for a year and a half and have had no problem with cracks.

What I have seen is that if you overtighten the head, the shaft does seem to bulge a bit at the end.

Perhaps your inserts were put in incorrectly (the insertion tool is supposed to prevent that, but I wouldn't put it past some shops from finding their own way of inserting them that might not be ideal.)