well it will only cost you 99 cents to test if subscribing fixes the issue, - and you can probably force an apple refund if it doesn't
surely the developers and the initial testers will have tested with >40 books
also - you tested 2 libraries using wireless device. have you/can you test using connect to content server
how many books are in the library that you are trying to sync. and have you ruled out the possibility that the app runs out of storage after 40 books - unlikely but check anyway?
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