In the case of your second book, the package identifier is an ISBN and
you presumably deleted the ISBN from the identifiers in calibre. So
calibre has to delete it from the OPF when applying the metadata to the
file. I suppose I could add some code to replace it with a randomly
generated UUID in this case to keep Check Book happy.
In the case of your second book, the package identifier is an ISBN and
you presumably deleted the ISBN from the identifiers in calibre. So
calibre has to delete it from the OPF when applying the metadata to the
file. I suppose I could add some code to replace it with a randomly
generated UUID in this case to keep Check Book happy.