Index: library/Zend/Controller/Router/Route/Regex.php
===================================================================
--- library/Zend/Controller/Router/Route/Regex.php	(revision 8431)
+++ library/Zend/Controller/Router/Route/Regex.php	(working copy)
@@ -132,7 +132,7 @@
 
         return $return;
     }
-
+    
     /**
      * Assembles a URL path defined by this route
      *
@@ -146,13 +146,13 @@
             throw new Zend_Controller_Router_Exception('Cannot assemble. Reversed route is not specified.');
         }
 
-        $data = $this->_getMappedValues($data, true, false);
-        $data += $this->_getMappedValues($this->_defaults, true, false);
-        $data += $this->_values;
+        $mergedData = $this->_getMappedValues($this->_defaults, true, false);
+        $mergedData = $this->_arrayMergeNumericKeys($mergedData, $this->_getMappedValues($this->_values, true, false));
+        $mergedData = $this->_arrayMergeNumericKeys($mergedData, $this->_getMappedValues($data, true, false));
 
-        ksort($data);
+        ksort($mergedData);
 
-        $return = @vsprintf($this->_reverse, $data);
+        $return = @vsprintf($this->_reverse, $mergedData);
 
         if ($return === false) {
             require_once 'Zend/Controller/Router/Exception.php';
@@ -183,5 +183,23 @@
     public function getDefaults() {
         return $this->_defaults;
     }
+    
+    /**
+     * _arrayMergeNumericKeys() - allows for a strict key (numeric's included) array_merge.  
+     * php's array_merge() lacks the ability to merge with numeric keys.
+     *
+     * @param array $array1
+     * @param array $array2
+     * @return array
+     */
+    protected function _arrayMergeNumericKeys(Array $array1, Array $array2)
+    {
+        $returnArray = $array1;
+        foreach ($array2 as $array2Index => $array2Value) {
+            $returnArray[$array2Index] = $array2Value;
+        }
+        return $returnArray;
+    }
+    
 
 }
Index: tests/Zend/Controller/Router/Route/RegexTest.php
===================================================================
--- tests/Zend/Controller/Router/Route/RegexTest.php	(revision 8431)
+++ tests/Zend/Controller/Router/Route/RegexTest.php	(working copy)
@@ -5,12 +5,11 @@
  * @subpackage UnitTests
  */
 
+require_once dirname(__FILE__) . '/../../../../TestHelper.php';
+
 /** Zend_Controller_Router_Route_Regex */
 require_once 'Zend/Controller/Router/Route/Regex.php';
 
-/** PHPUnit test case */
-require_once 'PHPUnit/Framework/TestCase.php';
-
 /**
  * @category   Zend
  * @package    Zend_Controller
@@ -391,7 +390,10 @@
 
     }
     
-    public function testAssembleZF2301() 
+    /**
+     * @issue ZF-2301
+     */
+    public function testAssemblyOfRouteWithMergedMatchedParts() 
     {
         $route = new Zend_Controller_Router_Route_Regex(
             "itemlist(?:/(\d+))?",
@@ -400,15 +402,20 @@
             'itemlist/%d'
         );
         
-        $values = $route->match('/itemlist/2');
+        // make sure defaults work
+        $this->assertEquals(array('page' => 1), $route->match('/itemlist/'));
         
-        $this->assertEquals(array('page' => 2), $values);
-
-        $url = $route->assemble();
-        $this->assertEquals('itemlist/2', $url);
+        // make sure default assembly work
+        $this->assertEquals('itemlist/1', $route->assemble());
         
-        $url = $route->assemble(array('page' => 2));
-        $this->assertEquals('itemlist/2', $url);
+        // make sure the route is parsed correctly
+        $this->assertEquals(array('page' => 2), $route->match('/itemlist/2'));
+        
+        // check to make sure that the default assembly will return with default 1 (previously defined)
+        $this->assertEquals('itemlist/2', $route->assemble());
+        
+        // check to make sure that the assembly will return with provided page=2 in the correct place
+        $this->assertEquals('itemlist/2', $route->assemble(array('page' => 2)));
     }
     
 }