[Graham]

It's a funny one, do you want to give Class A cars a better chance of actually winning a couple of events then it makes sense to allow lightweight windows along with the currently allowed interior and motor swaps.

It doesn't bother me as all my cars have the original windows...and they do OK

I think in Mikes case he is not trying to improve the competitiveness of his car with "alternative glazing" 
It's just he misunderstood that cars fitted with interiors have to be visible