Problem with Material Instance normal map parameter

I’m having an issue whereby when using a material instance constant of a base material, I’m seeing very different results compared to a standard material using exactly the same texture inputs:

The cube on the left is using a material instance constant and the cube on the right is using a secondary base material with exactly the same texture params as the mat inst.

This issue only seems to occur if the normal map in the first base material differs from that being used in the mat inst that is instancing it.

Here’s a sample .upk showing the issue:…iLzwxXs7Ap8HEG

The two cubes should look identical, but are wildly different. Anyone know what is happening here?

I opened your upk I see what you mean. I added more boxes to the material with a snow parameter and when I did that I made them look a lot closer to the same.

But the point is that they should be exactly the same if the mat inst is using the same texture inputs as BaseMat2.

It seems that both normal maps are being use. Even tho you just checked it to use the 2nd one in the instance, like they seem to be combining.

Exactly. This seems like a major bug. I have some materials that use normal maps where this doesn’t happen. Not sure why this normal map causes this issue. This normal was created via the speedtree app.