I have been having this issue in WvW. It seems to occur during fights where I have either had conditions or immobilize applied and after the effects have worn off I am rooted in place with no conditions on my character. I am only able to unroot myself by using sword leap, then everything is normal. This is a terrible bug in WvW, especially if you are unaware of whats happening because you are rooted and your opponent is free to beat you into oblivion.