Technically, it’s not a bug, but the normal behavior of the sort:"string", as empty strings move up or down the list depending on the sorting direction.
You can avoid this by using sort:"int" (for the particular case) or any custom sorting function.
This behavior, I have already observed, but I can not make sort:int, because, the data will be always string, but my question here is, if the there is no data in the column, on what basis it is sorting and why it is sorting?.
if we want to restrict also , can you please share some demo code so that we can do the same.