Yeah, it's the rubbery paint. It degrades over time and goes all sticky, and this seems worse for certain colors/batches.

Most of the older MX-850s I've felt with the less tacky black paint haven't gone bad like that - but it certainly happened to the MX-700 with its dark blue paint, AND the beige paint on the front.

Seems to happen quickly for previously used remotes that don't get used for a while - maybe something to do with old skin oils.