Grimrock

This is what happens when i place stairs on a level..

http://imgur.com/a/InBhT

the 3rd image is what it looks like when you go down the stairs.. You clip through the floor..

They are all messed up heres the level design..

http://i.imgur.com/8CVmzdV.png first floor

http://i.imgur.com/ssUaqst.png second floor

Stairs need to be surrounded by walls on all sides but the front. I'm not sure if secret doors can be used as pseudo-walls for this purpose.
If you don't place walls around (including on corners) thats what you get.

Walls of the side should be as easy as putting secret doors on the side of the stairs, but I can't think of a way to correct the floor behind it.

It's fairly simple:

While the editor OBJECT for stairs seems to be only 1 tile big, the staircase is actually 2 tiles big (in the direction of the stairs) That's why the game requires WALL behind the stairs, which gets replaced by the stairs' second half in runtime.