> IMO it is a bug in POV-Ray. The ray passes through the box and is
refracted
> when it leaves it. That means it is refracted even though the ior before
> the hit and after the hit both are 1.0.

This is not a bug, it is the intended operation as AFAIK.  Even though ior
is specified in 'interior'  it isn't treated as an interior property but
rather acts only on surfaces.  This is whay you can't have ior mapping or
variable iors within a single object.  When a ray passes through a surface
it is refracted according to the iors at that surface.  In your example only
the surface of the intersection that belonged to the box with an ior of 1
has an ior of 1, the other surface has the ior of 1.2 so when the ray hits
this face, with the 1.2 ior, it gets refracted as if the interior had an ior
of 1.2 and the exterior had an ior of 1.

-tgq

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