Please keep in mind that in a dynamic zone update the changes are saved in the journal file. If you want to dump the changes into the zone file, you need to freeze the zone and then thaw (unfreeze) it. E.g.
rndc freeze example.com
rndc thaw example.com
Do note also that the above method is used in the case you want to manually edit the zone file and it's better not to use it for other reasons.