A bug that affects wall mods

[Jibbles]

I apologize if this has been posted before. 
But I'm making this post cause I don't recall having this issue in previous versions.

When you plan/build a vanilla wall, you're able to place a door/vent etc over them. 
But I've noticed with my wall mod AND several others that it won't let you do that anymore.
It pops up with "space already occupied."
I feel like this sort of a vanilla bug cause I believe it will affect any mod that's adding walls.
Should it be posted in normal bug section?

[Razuhl]

You might be able to avoid the problem. Declare a copy of your wall and set its "building.smoothedThing" property to your original def. That way the original wall should be able to use the hack that was added for smoothed walls.

Other than that it's not possible to define a new wall. Walls have no specific property that identifies them as such. They count as normal buildings. The game identifies just one building as a wall and thats hardcoded to the definition with the identifier "wall".