Issue Summary

It is possible for a Tag field to contain data which it will not display or indicate in any way.
Fields that contain data like this will be filtered as if they have a value, even though they do not appear to contain a value.
Exporting the database with these hidden values will not contain the hidden data.

Steps to Reproduce

1. Create a new database

Route 1:
step 2. create a CSV that will import data that would work as tags in a tag field.
step 3. Import the CSV. The Tag field will import as a text field.
step 4. Change the field that should be a tag field from text type to tag type
step 4a. note that the field will appear empty for all rows unless you add a tag.

Route 2:
Step 2. Change the tag field to a text type.
Step 3. Populate some of the rows with text in the tag field that currently accepts text.
Step 4. change the field type back to a tag field.
step 4a. Note that the field will appear empty for rows where the text does not match a tag registered for the field.

Step 5. Apply a filter to filter the new tag field as "is not empty".

Expected Results

The filter sees the fields that do not display any tags as being empty and filters them accordingly.

Actual Results

The fields that contain a value when the field is changed to a text field are treated as not being empty even if the row does not display a tag.

Workaround

Currently, the only workaround is to manually remove any extra data from the field.
Setting a tag and then removing the tag will fix an individual row.