Yeah, if the slab had no wall on top, it wouldn't be a problem, but in this case
it means I have to have all my walls at -0,02 m under the story level (instead of having it at story level) so I can get the correct effect. It shouldn't be that way, it should intersect correctly the way I'm trying to do, but unfortunately I checked on Archicad 17 and 18 and it's the same, so it's not a bug on archicad 19. It's something Graphisoft should fix