[cptxguys]

We have the same problem on our 2004 unit. It appears the 'paper' facing on the wallboard material has delaminated from the wood. It's occured on two of the four pieces on the perimeter of the shower skylight.

We're assuming it's from the moisture of the shower.

I don't imagine there's any way to seal the inner skylight against the ceiling material, so for now, we're going to live with it. When it annyoys us enough, I'll drop the inner skylight and re-glue the paper with 'waterproof' glue.