Description

When having a legacy widget added in the standalone editor saving works. However, when moving to the Customizer and editing the legacy widget, publishing changes fails with the error Unable to save due to 1 invalid setting.

Step-by-step reproduction instructions

0. Have Gutenberg trunk and TT1 theme active
1. Install and activate the Site Origin widgets bundle.
2. Go to Appearance > Widgets
3. Add a heading block.
4. Add a legacy widget, pick Site Origin Button Widget
5. Edit the legacy widget - set button label - and save the changes
6. Go to Appearance > Customize > Footer
7. Edit the legacy widget - change the button label
8. Publish
9. Notice the error on top of the sidebar Unable to save due to 1 invalid setting.

Expected behaviour

Changes are published.

Actual behaviour

Changes are not published.

Screenshots or screen recording (optional)