@package only fills from the default queue. If you're using
order sets its not going to work unless, as you figured out, you
re-add the order to the default set. For you this is happening when
you add the order in details mode. The workaround for what you're
doing is to keep the things you want to show up on your "proof",
being what they've ordered I'm assuming, in the default set until
you're done printing.
We ran into this problem early on and just adjusted our workflow to
not require order sets until order packlists were printed and
everything was shipped.