"Configure controlport automatically" is mysteriously missing when Vidalia couldn't start Tor
When a Windows user is running Tor already and starts TBB, it fails to start Tor because Tor can't bind to 9050 / 9051. When this happens, Vidalia chooses not to display the "Configure controlport automatically" button on its Settings -> Advanced page.
The workaround for people who want to run multiple Tors is "close all your other Tors before starting TBB, and then tell TBB to switch to switch to auto". It would be good if Vidalia could handle this directly though -- i.e. if it failed to start Tor, still offer the option to switch Tor to auto.
A simpler approach that would still help here would be to leave the clickbox in, but grey it out if you don't want the user clicking it.