nuxeo-user-suggestion params property not displayed in the UI

I am adding a groupRestriction parameter to a nuxeo-user-suggestion (cf NXS-5580)

Problem:
1. Select the nuxeo-user-suggestion
2 Enter a value for the params property, for example: {"groupRestriction": "FSA"}
3. Save: You see the parameter
4. Switch to code => the parameter is there
4 Back to view mode (or just refresh the page) => the param is not displayed,d you feel like it was not saved.

See the screencast