WebEx used to do this and thankfully stopped. I would never quit WebEx. I'd just press Cmd-Opt-Esc to bring up the list of running processes and force quit it to avoid it both reinserting itself into my login items and also to prevent it from running the WebEx listener app. Like dude, I'm quitting this app. Why do you think I want to run the app again? WTF? Like I say, they've stopped doing that, but wow, what a shitty thing to have done in the first place.