How can I disable the random/auto keeping of apps in the Dock? Sometimes the Dock will keep an icon app in the Dock, even though I haven't set it as such, even though I've previously de-kept it in Dock after the first time it kept it 'for me'. 

Is there a way to turn this off it's a bit annoying?
go to "system preferences", then choose "Dock" and uncheck the "show recent applications in dock" radio button.