When using OpenVSPmac2.0.3 or earlier, the airfoil cross-section plot persists when you leave the Foil tab of the MS_Wing editor. This is a known bug. Until it is fixed, the workaround is pretty easy. Once you leave the Foil tab by selecting another tab in the MS_Wing editor, simply click on the component name in the Geom Browser (usually sitting just to the left of the MS_Wing editor). This will force a refresh of the MS_Wing editor window.