http://www.head-fi.org/t/87779/isopropy
h-plastics
The second post here seems to have the answer:
"What you seem to be doing is leaching the plasticiser out of the plastic piece and what you see as film are residual solids. I would recommend a less aggressive cleaner.
Ever notice the foggy film you see on the inside of your car windows? That is plasticizer evaporating from the dash and other plastic pieces. When I lived in the desert this was so bad that the dash would harden and ultimately crack. The only way to slow this down was liberal applications of Armoral type products and towels to keep the sun away."
It definitely looks like film. And I looked up the percentage of the alcohol I used...
91%!!
I usually use 60% - 75% alcohol so mine was very strong. There might be something in clear boys that make them crack more easily. The plastic definitely feels harder. I'm not sure if that's because it's glossy or not, but it does...