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So we are talking about the keycaps, not the aluminum underneath.

Normal wear and tear.
 
Is this also an issue with the 2012 MBA?

I replaced my late 2010 with a 2012 and have not seen any of the bubbling and cracking on the keycap paint.

PS: PS I actually have two 2012's one for work and one for personal, no issues with either.
 
Same problem here on several of my keys. It's never been exposed to extreme temperatures. (2010 MBA)
 
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