Steps to reproduce:
- Add a Structure with Text and Text Box fields
- Add a Template based on that structure
- Add Asset Publisher portlet to a page
- Click to configure AP
- In configuration, choose 'Web Content Article' from the Asset Type dropdown
- Choose the structure name as the Web Content Article Subtype
- Flag the Filter by Field checkbox
- Click the Select button
- Click the radio option for Text field
- Click Save
Save will take effect.
Saving the filtered field option puts the portlet configuration in limbo and doesn't save. See screen record.