Well, I can only speak for my phone when I say that Tasker works as designed with the Kill App function, I just needed to insert a short wait after the bluetooth state change. Wouldn't work before that. I've used the function with both PodCast Addict and Waze and it terminates both apps after bluetooth disconnect. I'm running KitKat on a stock (unrooted) Moto X.
I set up a profile to detect bluetooth connect with a task to vibrate the phone for .2 seconds, so I confirm the profile is active. Then I created an exit task to 1) wait 10 seconds and 2) Kill app, Podcast Addict. I didn't need any plugins, root permissions, or third party apps to do it. Works every time, as designed.
I don't know why people are saying that tasker is misleading, or android doesn't allow 3rd party apps to kill other apps. I use Advanced Task Killer (manually) on a regular basis and it has no problems killing apps, and it's a third party app killing other apps... Tasker is doing the same thing, and on my phone, works as designed.