Invisible collision hulls that aren't doing a good job of colliding!

[G-Man]

Ok, I've got a staircase of invisible collision hulls for a masked texture staircase. Thing is when I play test the level I fall through certain collision hulls. Even funnier is that it is "half" of the collision hull that is letting me fall through. The other half is fine! I tried deleting the collision hull and then putting in another one but still the same problem. Any ideas?

[Aphex]

Make sure none of them are touching any other brush.