I recently had a Rattray Morta pipe develop a longitudinal crack through the bowl and extending into the stem, but it did not separate into two pieces. I had maybe smoked it a dozen times and had not mistreated it. Smoking Pipes gave me full store credit for it even though I had had it just over a year.
The only real mistreatment that could cause a split like that is letting a cake get too thick. Sitting on them (as one customer did) doesn't help either lol.