When changing Aspect Ratio Correction setting in the launcher (global options) the change is not taken into account in the Launcher until you quit or start a game and return to the launcher. Also when starting a game that uses the global options, if the aspect ratio correction setting has been changed just before starting the game it is not taken into account (you have to return to the launcher, at which point it is taken into account, and start the game again).
The same behaviour occurs also for the Fullscreen setting.
The change should either be applied immediately (when clicking on OK) or when changing the setting you should get a notice (e.g. "this change require restarting to take effect" in red below the options in the graphic tab) .
This was noticed with ScummVM 1.00svn42499 on MacOS X 10.5.