Help -- portal lasers not working based on where they're placed?

[reverendanthony]

I want to bar the player's way with lasers, so I've set up a hallway with two laser emitters like so:



However, I've run into a problem. The bottom laser works fine and causes damage to anything that hits it, while the top laser might as well not exist -- it looks as if it's a functional laser, but you just clip right through it without taking damage.

I've deleted and remade the laser, deleted the nonworking laser and simply moved the working laser into its position, but for some reason any laser in that particular spot will not harm the player nor impede his progress.

Does anybody know why this is?