iBooks won't update the book

[ndfred]

If a new version of the book is generated, iBooks or iTunes won't update its version when the new ePub file is dropped / downloaded. What I've tried so far:

• changing the contents of content.opf to refresh the package-file-hash property in the iTunesMetadata.plist file: a new instance of the book is created
• adding an itemId property to the iTunesMetadata.plist file and then touching package-file-hash: the new version is ignored
• changing the itemId property in the iTunesMetadata.plist file: a new instance of the book is created