What? π² No, I'm not saying that. The highlighted area should be two parts, but it didn't slice through. The lines are there, but it's still two separate areas!!!
intersection.png
It doesn't matter if it's a solid or not. It still doesn't slice through.
I've attached a simplified example.
If I do intersect-with-model on the bump that hasn't been cut out (the same one in the picture), it won't split.
Edit: I noticed that after splitting, there was a single polygon where the outline formed along the surface of the main object that was not cut . When I drew a line cutting it (the polygon), the bump shape separated immediately in two. I don't know why Dave didn't experience this: nocut.png
notasolid 2.skp