Saxon

There appears to be a bug in the method IntHashSet.copy(). The new IntHashSet that emerges from the copy appears to have all fields identical to the original except for _mask, and the difference in the _mask value means that existing entries are not found in a contains() call.

This is code that has been stable for years, and it's not obviously unused (though that might turn out to be the case). Perhaps it only happens under rare conditions in terms of the actual map content. The bug was revealed in a new piece of code in 10.0 that makes use of IntHashMap. As it happens, the new code doesn't actually need to invoke copy() at all.