One weird normal map error.

I found this weird error when I was using a normal map in Maya.

If you attach more than one bump2d node to a single file node and use these bump2d nodes as a normal map, whether set to Tangent Space Normals or Object Space Normals, this will cause a problem.

The object's color doesn't show up and the surface normals get messed up.

 

Here I have a simple shader connection.  A blinn shader with one normal map input.

The render looks like this.

I  create a new shader and used the same file node as a normal map through a new bump2d node and assign this new shader to the right plane.

 

And the render looks like below. It ruins the both shaders.

The surface normal became wrong . Not only that the surface will lose its diffuse color.

Had it not been for reflection, it would've looked like the following.

This problem only exists in Mental ray. Maya software works fine as expected.

In conclusion, one must not attach more than one bump2d node to a file node, if it's for normalmap.

Instead, one can feed multiple shaders with one bump2d node like below.