IOR in Blender Internal (raytraced) I'm confused about IOR in Blender Internal as used in raytraced transparency.
To demonstrate my issue, I set up a camera looking through a transparent sheet with IOR>1 (and slightly tinted) at a textured surface.
You can clearly see the expected refraction.

But when I flip normals, I get exactly the same render!
My question is therefore:  How does Blender Internal determine the "in/out"-side if it does not use the normals for that?

Placing the camera inside a properly closed transparent volume with IOR does not change anything.

Clearly, I can invert the IOR to treat camera rays, but I came across this issue when reflections going out and then back into the glass material misbehaved.
From user2859's comment:


  It doesn't use normals to determine where the ray is. It just swaps a traversal flag on ray pass.