For what it's worth, not all melamine boards appear to be the same in this regard. I covered a wall of my office in 4x8 sheets from Home Depot. It held up great. So a few months later I covered another wall, but bought the melamine from Lowes this time. The stuff from Lowes was borderline useless after a few weeks.

Dunno how useful this is as I have no idea how to identify the actual brand/manufacturer of the "good" ones...