Try momentarily switching your Mac's Display resolution to something really low. You should then see the bottom of the panels. Drag them in and up so they're small. Switch your resolution back to what it was, then drag the panels back to taste.
The only time I've encountered it is when working on a project with a dual display setup of differing resolutions, the panels enlarged to fit the larger, having then ported the project over to a single monitor system of lower res.