I just checked again. Different behavior than what I experienced yesterday. Or maybe I overlooked something yesterday. However, to clarify:
Editing an existing entry, whether single or multi, new or old upload shoes all shoes. The expired ones are greyed out though. Not bad, but not great:
Creating a new entry however only shows currently available shoes. This seems preferable to me. I only see this behavior for an entry that has not yet been saved:
Maybe this isn't a "bug" per se. Maybe it's a "feature."