Don't ask me, as i said, i never noticed abnormal normal map behaviour in Corona. As long as you set-up it correctly (gamma, space, tangent basis, handedness, etc.), default strength of 1, should always provide correct result. The only exceptions i can think of, is when you use normal map for special effects, like flakes in metallic paint, or when a normal map is arbitrary authored crap, or when you use it in combination with displacement. In any case, if you observe incorrect normal map behaviour, then at very least you should attach some examples how it looks. Providing offending texture would be even better.