Setting up tree_root in eZ Publish 5.1 has no effect on links inserted on XmlBlock fields, rendered with twig through ez_render_field.

steps to reproduce:

. On an eZ Publish 5.1, with eZ Demo layout, create a folder, on root node. Name it MyRootFolder. Check it's NodeId. (let's call it <rootFolderNodeId>)
. Within this MyRootFolder, create a new folder. Name it FolderA
. Within FolderA, create an article (MyArticleA -> <myArticleANodeId>)
. On FolderA, create a link to MyArticleA node in Description field. OE disabled shows something like:

<link href="eznode://<myArticleANodeId>">link</link>

. Configure the PathPrefix in ezpublish.yml

ezdemo_site_user:
  content:
    tree_root:
      location_id: <rootFolderNodeId>
  location_view:
    full:
      smallFolder:
        template: eZDemoBundle:full:small_folder.html.twig
        match:
          Identifier\ContentType: folder

Now, when you open the homepage of your front end, MyRootFolder will be presented. Open FolderA and this full view will be rendered through the twig example small_folder.html.twig

The link will be rendered as /MyRootFolder/FolderA/MyArticleA
The expected result would be that it linked to /FolderA/MyArticleA
If you remove the override setting, the folder will be rendered properly, but without going through ez_render_field of the xml block