System Information
Windows 7 64, HD 5770

Blender Version
Broken: 9337574 (2.71 release) + 35bc266

Short description of error
Shadows or materials or shading in Game Engine tend to have problems if Auto Smooth is activated.
The problems only seem to occur when the mesh object have minimum 2 material slots assigned and a modifier enabled.

I think all Generate modifiers can be used.

Exact steps for others to reproduce the error

• Add a Lamp>Sun
  • Rotate it Y90° or how you like.
• Add a Cube.
  • Give it a Array modifier > Arrays 3 or more.
  • Go to Properties>Object Data>Normals: enable Auto Smooth.
  • Give it 2 Materials and assign them both on Cubes faces.

• Press P to start the Game Engine.

Problem: There are random dark and bright faces on the geometry.