yeah, the looking at the drop-down from the top of you youtube homepage, it'll say that your watch later playlist is empty, and when you try to add something to the list, the playlist at the bottom appears to not have anything in it. After messing around with this a while, I realized that if you press "view list" on your watch later at the top of the page, your playlist will come up on a new page, but it may be out of order and wrong, which you can fix by opening another window, and adding another video to the playlist, and reloading the watch later playlist window.