nuxeo-directory-suggestion and custom "params" mishandled and mis displayed

• Go to ui > layouts > Built-in Document types > file > edit
• (Configure if needed)
• Click the "nature" widget
• Add a params: {'contains': true} (with the brackets)
• Save
• Open another layout
• Click a nuxero-directory-suggestion
  => You have this {'contains': true}
• Open another one => same. Looks like all nuxeo-directory-suggestion now have this value
• Now, explicitly empty it and set another parameter of the widget and save
• open the initial file edit layout:
• "params" property is empty
• But if you look at the sources it does contain the special parameters

Also,