Messed up increments when dragging regular parts on union parts?

I’ve been experiencing this bug for a very long time. Recently, the problem has been getting on my nerves because it is taking me extra time to re-adjust the positions of parts.

The bottom part is a (4, 1, 2) union. The top part is (1, 1, 2) regular part.
When I drag a regular part around on a union part, the position of the regular part gets messed up.

Before the bug, this is what I would get if I dragged the regular part onto the union part.