Originally Posted by kovidgoyal
Use the normal add mechanism for such books. Supporting multi file books in auto add is highly problematic. There is no way to know when all the files of the book are available. calibre will be notified the moment the first file is copied, it then has no way to know how long to wait until all the remaining files have been copied.
While not fixing this issue exactly, how about a 'Folder Poll Interval' Tweak?