Belt Staining

So this one is new to me.

I have a really habit of buying figures and then letting them sit boxed up for like, a month before I open them. Back at the end of August (I think, just based on when I was frequenting the Wal-Mart in question), I picked up the RA series Brock Lesnar. I finally got around to opening him last night. The figure is great, I really like it a lot, no regrets about eventually having character duplicates when I get the UE eventually, but one of the first things I noticed was a small, relatively harmless but still noticeable black stain on his shoulder where the belt is slung over it in the package. It's almost identical to the soft goods stains I've seen from other figures packaged wearing a shirt or whatever, but I've never seen it with a belt before.

Has anyone encountered this? It's not a deal breaker or anything - it's a very innocuous mark, but it does kinda make me wanna go back to figures I've had displayed with black strap belts and see if that's caused any issues.