System Information
Bug is present on multiple computers with different operating systems and graphics cards.

Blender Version
Bug is present in multiple builds including 2.71 and multiple daily builds up to c670ceb

Short description of error
the "inner face thickness" setting for detecting cloth collisions (bpy.context.object.collision.thickness_inner) has no effect.
The collision margin is therefore determined exclusively by the outer face thickness setting. Here is how it's supposed to work: http://wiki.blender.org/index.php/Doc:2.6/Manual/Physics/Collision

Exact steps for others to reproduce the error
Set up any cloth with a collision object. With any point of the cloth on the side of a face in the collision object opposite the direction of the normal, the cloth moves away from the face rather than moving the direction of the normal when within the "inner face thickness" margin. It doesn't matter if the cloth starts inside the "inner face thickness" margin or moves into the margin.
for the attached file, start the cloth simulation and observe the different "inner face thickness" margins on the collision objects.