Capsule Collider / Mesh Collider: Goes through walls, doesn't fall through floor?

Hello,

I'm pretty sure my player never went through the walls before, but now all of a sudden they are. I'm not sure what I changed to allow this. The player Capsule Collider doesn't fall through the floor, but the player is able to walk through walls. This only is on the large mesh colliders -- the player is still stopped by smaller boulders and rocks w/ mesh colliders.

Here's a video -- the fireball at the start explodes upon contact with the wall (onTrigger attached to the particle itself): http://sfbaystudios.com/mesh.mov

But then the player walks through.

The physics colliders are fine, set to collide between the map and the player (after all, the player isn't falling through the floor). Any ideas?

Thanks!!