Installed the example from bug 110742, configured this icon set in tools > options > view > icon set, and removed the extension. This results in tango_testing, which is the next in the list in master. We better switch back to automatic.
And when a user installs an icon set extension she likely wants to use it. So how about automatically switching tools > options > view > icon set on install?
I support both ideas.
But instead of switching automatically to the newly installed icon set, the user should be asked if he want to use it immediately or later with the options dialog.
I'm for switch back to automatic next in the list is at least not really usefull.