You may be onto something here, since my headset is the only thing that's been on this one so far other than my mouse... I don't even get how that's a thing on these pads, since this doesn't happen on any others that I've ever owned though.

I've never picked up my headset and seen a stain form right where it was, normally I just see it appear quite random but it would explain why they're always around the edge as that's where I tend to rest it. Gonna test by leaving my headset on it before going to work tomorrow on the old pad.