"post-duplivert mis-behaviour"

There’s a strange thing about dupliverted objects - it’s a problem I’ve come across a few times, and I don’t know if it’s a bug or if there’s something I’m missing. When I make dupliverts real, they seem to be separate objects, but not entirely. In object mode they are like separate objects, but I can’t join them, and when I enter edit mode with any of them, all of them are edited. I make sure none of them is parented in any way, I try to clear all dependancies, I remove the original object and the reference object, but on some level they are still connected. Any ideas?