I'm having the same issue with the last two updates. Walls show up as opaque across all floors. On the elevated floors when I complete the room it makes the "floor" gray, so it blocks them out, but on the lower floors, walls above look the same as walls on that level. They used to be light blue.
I tried the tip above and it didn't work.
Out of curiosity I tired spacing the floors out, ie I put the elevation of the upper floor higher than the wall height below, this did not work. I also tried using 3-d view to put a ceiling on the ground level, even then, walls from the upper floor show up as opaque on the lower floors.
With the last update roofs are really messed up too. This program crashes all the time on me, but at least it would "recover" unsaved work. Now it isn't even usable.
