weird normal map

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FFX Runner 2 Undead Rods

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Published on December 4, 2015 9:46:06 AM ● Video Link: https://www.youtube.com/watch?v=J2-jXHsTvI4

Duration: 0:24

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anyone noticed a weird normal map behavior when set by shader material?
here two copy of the same model sharing the same normal map with the only exception of how it is assigned to them. There is a directional light, set to 45 degree, who is lighting the scene.
Normal map on the left model is set by using built-in fixed material while the normal map on the right model is set by using a shader material like this:
uniform texture normal_map;
NORMALMAP = tex(normal_map, UV).xyz;
NORMALMAP_DEPTH = 1;

as you can notice the model with fixed material looks natural while it is revolving while the model with shader material shows a weird shading artifact, a bit like if the light was moving vertically.