I have just added all my books to my owned list, but I found I had duplicated some (note sure how). Having a warning when adding a book with something like
'you already have another edition of this book marked as owned would you like to -cancel adding this edition, -replace the edition on your list for this one or -add this edition anyway.'
With each hyphen being a button. This could help prevent accidental re-adds while still allowing it to happen (i have multiple copies of the same book, so I know some people will need that)