I've came to an edge case.

I'm tracking changes for an ISet<T> and, for some project requirement, I need to clear it and re-add all items in order to re-hash them internally in an implementation like HashSet<T>.

Currently, if I call ICollection<T>.Clear`, items will be cleared, but tracking information will still say that I've removed some items, and I've added some of them. In my particular case, if I had 3 items, clearing the collection ended up in having 6 added items (because they're the same items with a different hash code).