I visited a local Utah music store today and half of their solid tenor ukes looked as if the tops had shrunken just a bit and pulled the neck down, resulting in high frets where the neck joins the body (not a real back bow like I've seen on some guitars, but moving in the same direction). The repair guy told me it happened regularly through the dry winters. With a little fret leveling they will likely play fine, but that fretboard will never be completely flat again. They were on wall display hangers, so I suppose were victims of the ambient indoor humidity. Have those of you with cold dry winters seen a lot of this?