It would make sense that when the 'Navigate to the first link automatically' option is selected for a tabbed menu, that the crumbtrail and back link are automatically hidden, as I cannot imagine any scenario when you would want to display them and it would save having to do it with CSS or Javascript
Very easy with CSS too as you said: replace with your scene number
div#kn-scene_341 div.kn-view.kn-back-link > a {display:none;}