I had this problem happen because of Jungle Formula insect repellant. It is very corrosive stuff...it took all the markings off my Silva compass and also melted the plastic a bit...the knife I had at the time was a Blackjack Maurader which came with a Res-C grip...here is a pic...



I sorted it out by rubbing the handle in washing up liquid and giving it a good wash/soak in warm water then rinsing it for a good bit. The rubber that had soaked the stuff into it came away in small bits like dried skin and what was not touched under it was then OK...

Whichever way I cannot see washing it would cause any problems and would remove the chemicals if that is what might have caused the problem. It should'nt invalidate the warranty either. My best guess is that somehow this is chemical induced...super glue remover and some other chemicals like that can also have a bad effect on rubber...

I did'nt have much to work with at the time but there was some white staining on the rubber after this...I then got some black Kiwi Parade Gloss boot polish and gave the handle a good brushing with this...then polished it off with a rag...it was "perfect" after that...but maybe I just got lucky with the "weird" mix of soap and wax...