Well, if you're saving the database as a flat file, you'll want to chomp $borrower before you use it in an assignment, otherwise you're file will look like:

     Author's Name:Book/Borrower
     :Book:Book:Book 

rather than

     Author's Name:Book/Borrower:Book:Book:Book 

This would also explain why it looks like the author's other books seem to have been erased.