Yes. It's using a global variable to canonicalize instances so that reference equality is value equality. An LRU cache will evict things that are still in use, so that the canonicalization process returns a different instance for the same value. (If it doesn't evict anything still in use, it's strictly inferior to just tying to the garbage collector anyway.) This will break the assumption that reference equality is the same as value equality that the rest of the code depends on.