I bred cats, after making the kitten sit, I sent one of the parents away in a minecart. I then gave the kitten fish until it grew and then attempted to breed that cat with the parent.  The cooldown already passed, and both cats were "willing".  They bumped into each as the breeding animation does, but there is no kitten.  I have tried breeding them again 10 times to no avail.  Incest aside, am I doing anything wrong?

(This was working for a while, but then stopped working)