After some experimentation, I found the following. If you have an existing form that saves to MySQL and...

... you add a field, it will add the field to the MySQL database.

... you remove a field, it leaves the field in the database.

... you remove a field from MySQL that exists on the form, the form will add it back.

... you add a field to both MySQL and WFB where the MySQL field name and the WFB field name are the same and the fieldname is added at the end of the MySQL table, the form writes data to the database properly.

... you add a field to MySQL but not to WFB, the form will write the data correctly to the fields it knows and ignore the ones you added only to MySQL.

So, if I understand, you should add/delete/modify fields through WFB and let it do the work?

Hey, thanks for posting this by the way!

Yes, WFB will do the work. The fact to be aware of is that if you delete a field in WFB, it will remain in the db. If you want the db to match, you will need to manually remove the field.