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