Index: kernel/managers/rewrite_url_processor.php
===================================================================
--- kernel/managers/rewrite_url_processor.php	(revision 14733)
+++ kernel/managers/rewrite_url_processor.php	(working copy)
@@ -139,7 +139,10 @@
 			$passed = $vars['pass']; // also used in bottom of this method
 			unset($vars['pass']);
 
-			$this->_setCachedUrl($url, Array ('vars' => $vars, 'passed' => $passed));
+			if ( !$this->_partsToParse ) {
+				// don't cache 404 Not Found
+				$this->_setCachedUrl($url, Array ('vars' => $vars, 'passed' => $passed));
+			}
 
 			if ( $this->Application->GetVarDirect('t', 'Post') ) {
 				// template from POST overrides template from URL.