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I'd tend to think it's not actually on fire, as heat of that magnitude (enough to actually scorch the keyboard) would likely also fry the insides and make it pretty uncomfortable to type.

A couple of guesses would be either that there is some heat that is causing the silicone to discolor the keyboard, or the silicone is simply rubbing off a bit on the keyboard.

Let us know how the cleaning works.
 
Sorry...

I think I've spent too much time reading this kind of paranoia.
 
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