in the template file standard/templates/content/datatype/edit/ezuser.tpl
there is a form input element (on the 19th line):

<input type="text" name="{$attribute_base}data_user_email{$attribute.id}" size="17" value="{$attribute.content.email|wash(xhtml)}">

the empty tage should be closed (" >" -> "/>") inorder to render as valid xml