Steps to reproduce: 1) Set up several System Monitor applets, e.g. in the panel. 2) Open the configuration dialog of one of them. 3) Open the configuration dialog of another. Actual result: The dialog from step 2) is accepted and closed without asking (which also currently leads to Bug 429163). Expected result: Either a separate instance of the dialog should be opened, or the existing one should at least ask for confirmation before closing, because it might contain an unintended or incomplete setup.
Oof.
Just tested with today's git master. Now it discards pending changes rather than accepting them. Not sure if this is better or worse!