I can't find any listing for an 86D DDR so I'm fairly sure this is some sort of machine doubling. And I know, it's small - too small to see without good magnification... Worn die perhaps?
I think it has something to do with it having a zinc core. I come across quite a few like this and even some that are worse. Some that I find have deteriorated to the point where cracks appear in the areas that you point out showing "doubling effect". When the cracks appear in that area, the zinc core is exposed.