The org.nuxeo.ecm.user.center.UserCodec.getUrlFromDocumentView(DocumentView) by default quotes '@' character into '%40' but org.nuxeo.ecm.user.center.UserCodec.getDocumentViewFromUrl(String) does not decode it accrodingdly.
When username is email address containing '@' character, link to navigate to user view from the user widget might lead to page not found exception.
This is mainly reproducible with a local instance. A remote instance will be behind a reverse proxy or other network infrastructure which correctly convert the url. (For instance, you can't reproduce on demo.nuxeo.com)