[unboggling]

A couple months ago I mentioned I was losing some books occasionally during Save/Add operations to populate new empty libraries, with Automerge off, and Yes to add duplicates. I finally pinned down this behavior. It happens in Save To Disk from Library 1, not in Add Books to Library 2. Add Books can't find what Save To Disk didn't put there.

In two separate records, if Authors matches Authors AND Title matches Title, one of those records is dropped during the Save To Disk. This happens when the Authors and Title combinations are identical, independently of any other fields, including IDs. For example, 2 books are both Saved when they have identical ISBN13s and unique Authors or unique Titles; but 2 books are not Saved when Authors/Title combination keys aren't unique even when their ISBN13s are unique.

Copy To Library does NOT have this behavior, it Copies both records when their Authors/Title match.

This isn't necessarily a bug with Save To Disk, but it's something to keep in mind. The work-around for Save To Disk is: within any particular Authors, append something different to identical Titles to make each Title unique, such as "(from Amazon)" on one and "(from Gutenberg)" on the other. Or, use Copy To Library from Library 1 to Library 2, rather than a Save To Disk from Library 1 followed by an Add Books to Library 2.