That shot of the rear casement shows exactly what they did...fudged it! It looks like they spackled the corners with filler to cover the screw-up!
I get more disappointed with DML by the day. They did the same kind of fudge-fixing method in their T-34-767 kit. Just...sad.
Both earlier kits of the SU-85 and SU-85M have no problems here. I have built both.
I guess orange and black label = death now, like a scary halloween.