UV_pass on refractive materials missing some refractions

[gagui]

Hi!

While I was trying to make an UV pass of some textures seen throug refractive materials I've notice that some parts of the refraction was missing.
I reproduced an UV pass with gradients and didn't match with render element. So... whats going on here?

Image on the right is uv pass and image on the left is a diffuse pass made of gradients to simulate the uv pass.

[hermit.crab]

What's the texture version's shader setup? Could you attach the scene here?