My furniture... It's alive!

Your wood furniture may be a dead tree, but that doesn't mean that it can't still breath. Have you ever noticed that every once and a while your dinette doesn't always perfectly meet in the middle where the leaf goes? It will absorb the moisture in the air as well as let the moisture out when the air is dry. Nothing is wrong when it does this, it's supposed to. There are wood surfaces with baked on varnishes that protect against moisture damage but usually you will see that the underside is not baked on so that your furniture will stay healthily healthy and breathing.