Two objects use the same material, which is the 2nd material slot for the first object created.
The first object has (any?) modifier except Armature. eg. Subsurf works.
On one object the shared material does not show in BGE, the faces are invisible.
The material index isn't reset to zero for the modified mesh probably, this has happened before. But it only happens if the material is the same.
Windows Vista 64, NVidia GeForce GT 240, Blender 2.55 official, VBO off.
The tracker is down to 3 pages - awesome job everyone!