applications - Why are disabled apps still running?

I've noticed that apps (such as Google Contacts Sync) that have been disabled using the stock Android (KitKat) app manager still show up as running when using process observer tools. This is true even after the device has been rebooted.

Why are disabled apps still running? Is there an effective (and safe) way to actually disable them?

Solutions requiring root privileges are acceptable.

(Note that for the specific example above, you can tell Android not to sync your contacts, but it still runs the Google Contacts Sync process. But let's not dwell on that example... it's just an example.)