OCL25 — OrderedSet::insertAt unclear for insert of existing element

The pseudocode for OrderedSet::insertAt assumes that the inserted element is not already contained.

Presumably insertion of an existing element does not increase the OrderedSet size.

Design choice. Is the old element retained or is the old element removed and the new element inserted? The latter might preserve the postcondition that the element at the index is the inserted object, but what if the removed element was earlier so that everything moved along first?

Surely the only predictable behavior is that the old element is retained?