The 3D Preview shows small artifacts, specially the specular reflections?
To solve this, change the Normal Map Preview setting in the Options to “Floating Point”. The Normal Map Preview setting selects whether the normal map in the 3D Preview is rendered from an 8-bit map or from a floating point map. If you see artifacts, usually in the specularity, change this setting to floating point. The bad news is that using floating point might slow-down 3D previews after changing settings, specially in older 3D graphics boards. These artifacts usually appear in smooth materials.