I've experienced this bug on numerous occasions. I recommend placing all of your legendary, set items, and Unique items in the shared chest. Then, move to a different level. For example, if you are on Platinum, return to Gold and then teleport to Start Island, just to give the game a chance to reset. Afterward, try loading in Platinum again with all your "special items" still in the shared chest. This may allow you to "shake" him. Also, starting a new level usually fixes this issue. It's really sort of creepy having someone shadowing you like that, isn't it?
I hope this helps, ma'am.