Eclipse’s welcome screen causes this kind of bug in the editor specifically (https://bugs.eclipse.org/bugs/show_bug.cgi?id=426557). Sometimes you can find that when you restart can’t move with control+arrow in the editor but you can in other views like console window.
You can disable welcome screen ( in most eclipse based IDEs it’s a checkbox in the welcome screen ) and then restart eclipse just to be sure it won’t happend again. Everything will work again.