Honestly, going by code structure, that seems unlikely. If it was intended to be save-game specific, it would be stored in the save file… which there is absolutely no reason to load anything from if another one is loaded. A bug that accidentally loads data from another save file seems extremely unlikely. A bug that left data in memory when you load a save and then load another one would be imaginable though, but I think people would have noticed if the items were only available if you already loaded another save in the same session.
It would seem more likely to me that them not being shared is a bug, and nobody noticed or reported it yet.