Godot version: 3.0 59e83af
OS/device including version:
Windows 10, GF970
Normal map produce wrong results with inbuilt geometry.

Project:
crazy_normals.zip
Steps to reproduce:
Create MeshInstance and set mesh to 'new PlaneMesh' (or quad or box). Create material for it and add normal map. Add light into scene. Normal map will show incorrect results.