Custom values not correctly copied to revisions

I recently tried using this on a post that has non-singular metadata (i.e. there are multiple values for the same key, rather than storing in a singular array). It seems the revisionary_copy_postmeta function uses update_post_meta rather than add_post_meta, causing only the last value of the series to be saved.

I can work around this with a custom hook on revisionary_copy_postmeta but that shouldn’t be necessary.