Prior to OS X 10.9, you could manually edit application .plist preference files in a text editor. Mavericks introduces a new background process named cfprefsd that caches preference routines for Cocoa based apps, so if you manually change a plist file (even if the app isn’t running), it’ll likely revert to the original preference when you launch the app next. Some have reported the same behavior with using the “defaults” command in Terminal for making changes to .plist preference files.

To work around this, quit the app you want to make changes to, locate the process named cfprefsd in Activity Monitor that has the logged in user name associated with, quit this cfprefsd process (it will reluanch itself automatically), make your changes to the application’s .plist preference file, then launch the app.