nuxeo-user-suggestion does not load user in edit mode

Studio-side

1. in Studio create a custom document type with a custom schema.
2. add a custom property referencing a user/group directory (see schema1.png and schema2.png)
3. in Designer generate forms for the document type
4. replace the content of the edit form with the following:

   <!--
   `nuxeo-testdoc-edit-layout`
   @group Nuxeo UI
   @element nuxeo-testdoc-edit-layout
   -->
   <dom-module id="nuxeo-testdoc-edit-layout">
     <template>
       <style>
         *[role=widget] {
           padding: 5px;
         }
       </style>
       <nuxeo-input role="widget" value="{{document.properties.dc:title}}" label="Title" type="text"></nuxeo-input>
   
       <nuxeo-user-suggestion role="widget" value="{{document.properties.testdoc:userChose}}" label="Test" search-type="USER_GROUP_TYPE" selection-formatter="{{_selectionFormatter_user}}" ></nuxeo-user-suggestion>
   
     </template>
   
     <script>
     Polymer({
       is: 'nuxeo-testdoc-edit-layout',
       behaviors: [Nuxeo.LayoutBehavior],
       properties: {
   
         /**
              * @doctype TestDoc
              */
         document: {
           type: Object,
         },
   
       },
       _selectionFormatter_user(user)  {             
         console.log(user);
         var texte = '<iron-icon icon="nuxeo:user" class="avatar"></iron-icon>' + user.firstName + ' ' + user.lastName + ' (' + user.company + ')';
         console.log('_selectionFormatter_objContact : ' + user.username + '//' + user);
         console.log(texte);
         return texte;
       }
     });
     </script>
   </dom-module>
   

Server-side

1. synch the project
2. log in
3. create a user
4. create a workspace
5. create a document of custom type (see Studio part)
6. select the user previously created
7. observe the format is the custom one (see selectFormat.png)
8. save the document
9. edit the document again
10. observe the value is not formatted as expected (see unformattedSelect.png)

This should work without any additional development.