I could be minor water damage combined with poor construction. Not too diffcult to fix with reasonable carpentry skills.
I had the same problem with the cabinets over the dinette and sofa in our 02 325. We had a water leak last fall because of a rotted slide topper and a blade seal that had rolled in on itself for a foot or so. We took out the napkins, board games and books that were in those cabinets and left it to dry out.
At the start of this season we realised we had a mold problem and I decided to open up the cabinets to find how bad it was. It was widespread enough to warrant the removal of the cabinet assembly.
I was amazed to find that the cabinets were only attached to the 1/8" lauan plywood skin that was glued to the block styrofoam insulation in the slide-out ceiling. It was also a surprise to find that the cabinets had apparently been built up inside the RV, from sheet plywood and 3/4" square molding. It couldn't have been an installed sub-assembly the way it was put into place. There are three longitudinal steel tube beams running the full length of the slide, but they weren't used as the anchor.
Of the 16 screws (1/2" sheet metal screws) holding the cabinets up, only two of them actually unscrewed. The others just fell out after I'd taken the two fairly secure ones out and the whole assembly came down.
I wouldn't be surprised that the front cabinets, despite their seemingly well-designed internal bracing, aren't similarly attached to something flimsy. There's no evidence in our rig of those cabinets breaking away (yet) but the 25" tube TV is no lightweight!
I'm a firm believer in "if it's not broken, don't fix it", so I won't even look until the end of the season. I'm about half way through building replacement cabinets for the slide-out and they will certainly be better built and MUCH more securely attached than the factory installation was.
Frank and Eileen
No longer RVers or FR owners