i know, they're different elements. but walls could interact with beams with priorities settings, and also collums. I guess it should also interact with slabs. I think if this is how graphisoft made it, they made a serious mistake. Meanwhile, I've found out that walls and slabs couldn't interact the way walls do with other elements from this post:
http://archicad-talk.graphisoft.com/viewtopic.php?printertopic=1&t=33003&postdays=0&postorder=asc&&s...
turns out you would have to use SOE to achieve this, and my partner also found that you could also simply use right click > Bring to Front on the walls. This works on his pc computer but not on my mac.