How to reproduce:

1 - Import an FBX file that has an embedded material using a texture in its bump map.
2 - Change the import settings to use the MaterialDescription import for materials.
3 - Create an AssetPostprocessor.OnPreprocessMaterialDescription method that would change the material shader to a shader that is not using a BumpMap.

Result: A popup appears to ask the texture to be changed to Normal Map.
Expected: No popup appears because the texture is not used as a Normal Map in the end.