nuxeo-directory-suggestion does not resolve value in a task screen

Resolving directory fields in a task was fixed in NXP-26816.
There still remains issues.

1. create a schema with a directory field
2. use it in a document type
3. read it from the document in a workflow task with a code similar to:

   <!--
   `nuxeo-testvocabfromdoc-20190808110758390-approve-task-layout`
   @group Nuxeo UI
   @element nuxeo-testvocabfromdoc-20190808110758390-approve-task-layout
   -->
   <dom-module id="nuxeo-testvocabfromdoc-20190808110758390-approve-task-layout">
     <template>
       <style>
         *[role=widget] {
           padding: 5px;
         }
       </style>
       <div role="widget">
         <label>Directive</label>
         <div>[[task.directive]]</div>
       </div>
   
       <div role="widget">
         <label>Created</label>
         <div>[[formatDate(task.created)]]</div>
       </div>
   
       <nuxeo-directory-suggestion value="{{document.properties.testVocSchema:myVocabField}}" label="zelabel" directory-name="myTestVocab" readonly></nuxeo-directory-suggestion>
   
     </template>
   
     <script>
     Polymer({
       is: 'nuxeo-testvocabfromdoc-20190808110758390-approve-task-layout',
       behaviors: [Nuxeo.LayoutBehavior],
       properties: {
   
         /**
            * @task var_testVocabFromDoc-20190808110758390-approve-task
            */
         task: {
           type: Object,
         },
   
         /**
            * @schema dublincore
            */
         document: {
           type: Object,
         },
   
       }
     });
     </script>
   </dom-module>
   

4. use the same code in a view form:

   <!--
   `nuxeo-testdocvoc-view-layout`
   @group Nuxeo UI
   @element nuxeo-testdocvoc-view-layout
   -->
   <dom-module id="nuxeo-testdocvoc-view-layout">
     <template>
       <style>
         *[role=widget] {
           padding: 5px;
         }
       </style>
       <nuxeo-directory-suggestion value="{{document.properties.testVocSchema:myVocabField}}" label="zelabel" directory-name="myTestVocab" readonly></nuxeo-directory-suggestion>
     </template>
   
     <script>
     Polymer({
       is: 'nuxeo-testdocvoc-view-layout',
       behaviors: [Nuxeo.LayoutBehavior],
       properties: {
   
         /**
            * @doctype testDocVoc
            */
         document: {
           type: Object,
         },
   
       }
     });
     </script>
   </dom-module>
   

5. observe the vocabulary is correctly resolved in the view page
6. observe in the task page (for example an approve one) that the vocabulary is resolved in the task section but not in the document section (see unresolved.png)

Expected behavior: the field should be resolved no matter the context