gosh, I stuck the K (in Oberon cover) into my backpack yesterday, and when I got it out, there was a dark mark on it!!!
I'm sure there were only safe things in it, chewing gums and highlighters and tissue and wallet, so I can't understand what cause this........
and not just outside, it even went all the way into the inside
damn, I'm freaked out!
the mark outside is hard to be noticed, so I just attach a snapshot of the inside:
