Now that you mentioned it, I remember running into this. We would compute hashes out of some objects to compare for equality and it turned out we sometimes had

Now that you mentioned it, I remember running into this. We would compute hashes out of some objects to compare for equality and it turned out we sometimes had more collisions than expected (orders of magnitude more), but this wasn't really reproducible. That was when I found out that the hashing algorithm wasn't deterministic. (Of course, the underlying cause was that our hash code calculations were not good and we had to fix them.)