Alright, I know this line https://github.com/mozilla/popcorn.webmaker.org/blob/master/public/src/timeline/trackhandles.js#L34 is when the sort is started, so when the mouse is held down. That where I would add the 'grabbing' class

What about when the sort stopped? I cant seem to find that in this file. Is it located somewhere else? Because I can only find it here: https://github.com/mozilla/popcorn.webmaker.org/blob/master/public/src/util/dragndrop.js#L1083