See that blood mana at the center of the screenshot? I placed a Blood Sliner on top of it and it spawned to tiles to the south, crossing a wall tile. I mean, it's cool for me, I'm trapped in there, but maybe it was not the intended behaviour?
I think I get the idea though and think it's somewhat intended. We don't want monsters on mana and obviously not on walls, so this can happen. I suppose it could also just block it.... probably the way we will go in the future.