Well, I thought the list would be alphabetical but unfortunately it's sorted by the ID. At the moment there is no such function nor a workaround for. Haven't even recognized that as I don't have any boxsets in my database. The way that I would do it is to create a boxset and assign the movies to and then make the next boxset.
In order to achieve what is possible, you have to try the impossible over and over again. Hermann Hesse