In the newest snapshot for 1.20, if you press ctrl pickblock in creative mode to nab the block and its NBT data, doing this with a chiselled bookshelf with books in it then placing it back down, the books inside aren't shown nor can you grab them. however if you break the new chiseled bookshelf, the books you initially placed inside also pop out.
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We're tracking this issue in MC-48453, so this ticket is being resolved and linked as a duplicate.
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dupe of MC-48453