A lot of the programs under the control-center management have a poor design by not having a "cancel" or some other way of resetting changes to the default state. Take for example the keyboard shortcut editor. Once you change a key binding in there there is NO WAY to change your mind. You better not click on something you had not intended or you will be sorry. The same thing goes for pretty much all the applications part of the control-center. It is nice to see instantly what you change, but it is dumb to not be able to hit "Cancel" and get on with life. One could save the state of the user settings before launching a config applet and then offer the user the chance to revert to that last set.
Filed upstream as http://bugzilla.gnome.org/show_bug.cgi?id=94716