Aircraft Shadows / Surface Illumination

Hi,

I have recently repainted the 737-800.

All is good except that the aircraft's shadow is now on the same side that the aircraft's surface is being illuminated by the sunlight.

Example - in the mid day sun when the sun is above the aircraft, underneath the aircraft is illuminated by the sunlight rather than the roof/top.

Is this to do with the DDS file or the way the textures are flipped? Not sure how to correct it as it's a bit annoying.

Thanks,

Steve