that's very odd. Although I do agree, isopropyl alcohol is strong, I have used it for years on all my and my family's cell phones (70%) since I am a germophobe and its disgusting using other people's phone caked in months of facial oils... ugh, that's really disgusting.
I've never had any problems... except with the clear screen portion of my red eBay faceplate for my 6682. It gets cloudy if ISA falls on it, but the rest is unaffected. Strangely, the cloudiness will go away by itself after a few days of normal use (although nothing can clean or "buff" off the cloudiness). Weird.