We need to preserve a user's edits so that a re-render never causes dataloss because a re-render could happen for many reasons e.g. Sync syncing an address/card record in storage. Bug 1483425 may help for some cases. It's easy to test this by clicking the re-render button in the debug/dev panel after making changes to a field. You can also test by clicking the Save Visible Form button in that dev/debug panel when you have an invalid cc-number in the field (this will bypass front-end validtion).