Messy tags

[Ozy Mate]

I have been using digiKam for years. Thank you for such a capable 
software. I have 8.1.0 at the moment.

Recently, I wanted to re-organize the tags and unify the database and 
metadata (in files) the same.

This is what I did:

1. Synchronize tags from pictures metadata to database.
2. Corrected all the tags, deleted some unnecessary tags within Digikam 
(hence database).;
3. Synchronize tags from database to metadata.

So far so good.

But, just to check the result, I re-synced from metadata to database. I 
see that many of the tags in metadata came back to tag list.

So it seems that synchronizing from database to metadata just copies 
tags from database to metadata. It doesn't delete existing tags in metadata.

By the way, I had used Lightroom before digiKam. I see some references 
to Lightroom in metadata. Perhaps that is the reason. Not sure.

So, my question is how to get rid of existing tags in metadata so that I 
can cleanly sync from database to metadata.

Thanks.