It’s actually pretty rare. So much so, it didn’t even happen to Tully. What is more common is for magically constructed intelligence to contain vagueness in the spell that leaves room for magic to solve the problem of making a thing that does x, y and z, and that leaves open the possibility that magic’s solution will be to make it sapient enough to understand what it’s being asked to do and how to do it and when. It’s a bug/feature.
When Tully was created, the vagueness was in place on purpose and the results expected and accounted for. His growing into sentience was really more a matter of growing beyond constraints that concealed what was already there.