Here is a wild guess. Is it possible that $booklist_1{$id} are all references to the same hash?

How are you initially populating %$booklist_1?

To test this, run this code:

for $book_id (keys %$booklist_1) {
  print $booklist_1{$book_id}, "\n";
}
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You will get output like HASH(0x12345678). If you get the same line repeated, then all of your sub-hashes are in fact the same hash object.

I could duplicate your output when I pre-initialized all of the %$booklist_1 hashes with the same hash.