Override getName().

framework/Core/lib/Horde/Core/Prefs/Identity.php

@@ -170,6 +170,26 @@ public function prefsGc()
         }
     }
 
+    /**
+     * Returns the user's full name.
+     *
+     * @param integer $ident  The identity to retrieve the name from.
+     *
+     * @return string  The user's full name, or the user name if it doesn't
+     *                 exist.
+     */
+    public function getName($ident = null)
+    {
+        global $registry;
+
+        if (!isset($this->_names[$ident]) &&
+            !strlen($this->getValue($this->_prefnames['fullname'], $ident))) {
+            $this->_names[$ident] = $registry->convertUsername($this->_user, false);
+        }
+
+        return parent::getName($ident);
+    }
+
     /**
      * Returns the from address based on the chosen identity. If no
      * address can be found it is built from the current user name and

framework/Core/package.xml

@@ -39,7 +39,7 @@
  </stability>
  <license uri="http://www.horde.org/licenses/lgpl21">LGPL-2.1</license>
  <notes>
-* 
+* [jan] Use correct user name as a fallback for identity full names with existing authusername hook.
  </notes>
  <contents>
   <dir baseinstalldir="/" name="/">
@@ -3688,7 +3688,7 @@
    <date>2014-11-04</date>
    <license uri="http://www.horde.org/licenses/lgpl21">LGPL-2.1</license>
    <notes>
-* 
+* [jan] Use correct user name as a fallback for identity full names with existing authusername hook.
    </notes>
   </release>
  </changelog>