Let’s say one slab is missing in a blue print like this:
If you add the slab, it will not be integrated into the active blue print but into a new construction; in the pict below, the active blue print is the upper structure, the new slab isn’t part of it.
@Relyss, heuu, how to say that… 
This oddity (more than bug?) occur during a building template session, not during the edition of an existing template after placing it. So technically your modif on the title is misleading… 
Ok, I’ve misunderstood. I was just trying to add a more significative title, to differentiate the bug (since there are too many bugs reported for the building editor)…
But then, you were just using the building editor as normal, to save later as a template?
I’m lost now 
Because usually it works, the new slabs get merged with the existing ones 
In that case, no save (because no way to drop a blue set in water); thinking in it a bit more, perhaps this is water related only…
I have noticed this to. They will not merge building if the slab you added is on a level below the slab of the second building you are connecting to. It’s kinda hard to explain, will try to upload a picture when I get home.
