Index: dna-jcr/src/main/java/org/jboss/dna/jcr/JcrNamespaceRegistry.java
===================================================================
--- dna-jcr/src/main/java/org/jboss/dna/jcr/JcrNamespaceRegistry.java	(revision 738)
+++ dna-jcr/src/main/java/org/jboss/dna/jcr/JcrNamespaceRegistry.java	(working copy)
@@ -109,11 +109,7 @@
      * @see javax.jcr.NamespaceRegistry#getPrefix(java.lang.String)
      */
     public String getPrefix( String uri ) throws NamespaceException, RepositoryException {
-        // Check the standard ones first, ensuring that invalid changes to the persistent storage don't matter ...
-        String prefix = STANDARD_BUILT_IN_PREFIXES_BY_NAMESPACE.get(uri);
-        if (prefix != null) return prefix;
-        // Now check the underlying registry ...
-        prefix = registry.getPrefixForNamespaceUri(uri, false);
+        String prefix = registry.getPrefixForNamespaceUri(uri, false);
         if (prefix == null) {
             throw new NamespaceException(JcrI18n.noNamespaceWithUri.text(uri));
         }
@@ -184,9 +180,7 @@
         if (STANDARD_BUILT_IN_PREFIXES.contains(prefix)) {
             throw new NamespaceException(JcrI18n.unableToRegisterReservedNamespacePrefix.text(prefix, uri));
         }
-        if (STANDARD_BUILT_IN_URIS.contains(uri)) {
-            throw new NamespaceException(JcrI18n.unableToRegisterReservedNamespaceUri.text(prefix, uri));
-        }
+
         // Check whether the prefix begins with 'xml' (in any case) ...
         if (prefix.toLowerCase().startsWith(XML_NAMESPACE_PREFIX)) {
             throw new NamespaceException(JcrI18n.unableToRegisterNamespaceUsingXmlPrefix.text(prefix, uri));