Following many tests, a hint by Paul and a discussion in uktrainsim forum, here is how to deal with windows in KRS.
Here is the interesting part on the uktrainsim discussion:
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‘SteelixB’
The HST uses something like glass_nm.TgPcDx you’ll notice.
Like I said, all [b:1ow6jv17]_nm does is stop it being compressed[/b:1ow6jv17], therefore you don’t lose quality, so somewhere along the line, RSDL probably decided it would be best to use _nm to prevent compression on glass.
As to why you don’t have alpha, I’m unsure, but in material settings, [b:1ow6jv17]make sure transparency is set to none[/b:1ow6jv17]. Remember that transparency and alpha are two different things… transparency refers to either opaque and transparent (as in completely see through).
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Example:
[img:1ow6jv17]http://img156.imageshack.us/img156/633/image4hm7.jpg[/img:1ow6jv17]
Result in KRS:
[img:1ow6jv17]http://img156.imageshack.us/img156/5554/image5zr6.jpg[/img:1ow6jv17]