**System Information**
Windows 8.1, i5, Sandy Bridge
**Blender Version**
Broken: 2.73a
**Short description of error**
Lambert shading of face is wrong, changing different part of mesh corrects shading.
**Exact steps for others to reproduce the error**
Open {F145439}.
Press F12 to render.
Notice that both large faces are rendered differently.
**Setup of scene and explanation why I think this is a bug**
The sun is perfect white, and shines with 45 degree on the white object.
The material has no specular intensity and its diffuse color/intensity is perfect white.
By the Lambert model, the model should be shaded with cos(45 deg) = 0.707.
Only one of the faces is shaded with this intensity, the other is too dark (0.6224)
After removing one or both of the **small** faces right of the large faces, both large faces render with the correct intensity.