ZBrushCentral

Using lightcap - material changes when adding lights?

I’m trying to light my character for rendering, I textured it using Matcap white then polypainted it, but whenever I add a light cap light the material changes to some sort of metalic shine, is there a reason why this happens and how I can stop it doing this?

http://www.zbrushcentral.com/showthread.php?179282-Standard-Light-or-with-LightCap-Answered&highlight=Lightcap+matcap