Applications open on login when they shouldn't be
Yes - this can be disconcerting when you don't realize that the majority of the Apple apps save their system state and don't even need to be told to start or stop. You can have an app in the dock when it's not running and you can have an app running when it's not in the dock. (or the task switcher interface)

The simple way to reset this is to choose log out from the Apple menu and turn off the check mark below.



Then log out, log in and log out again and verify the status if the check is disabled and the apps do not relaunch. 

In some rare cases, this setting / preference could get corrupt, so I then turn it on (which is the opposite of what you want)- log out / log in - then turn it off  (what you want) and before contacting support. Most of the time, just exercising the button a couple times is all that's needed if someone isn't aware to uncheck the button when they log out.