Index: library/Zend/Form/Element.php
===================================================================
--- library/Zend/Form/Element.php	(revision 24514)
+++ library/Zend/Form/Element.php	(working copy)
@@ -1393,19 +1393,18 @@
                     if ($this->isRequired()
                         || (!$this->isRequired() && !$this->getAllowEmpty())
                     ) {
-                        $result = false;
+                        $value = '';
                     }
-                } else {
-                    foreach ($value as $val) {
-                        if (!$validator->isValid($val, $context)) {
-                            $result = false;
-                            if ($this->_hasErrorMessages()) {
-                                $messages = $this->_getErrorMessages();
-                                $errors   = $messages;
-                            } else {
-                                $messages = array_merge($messages, $validator->getMessages());
-                                $errors   = array_merge($errors,   $validator->getErrors());
-                            }
+                }
+                foreach ((array)$value as $val) {
+                    if (!$validator->isValid($val, $context)) {
+                        $result = false;
+                        if ($this->_hasErrorMessages()) {
+                            $messages = $this->_getErrorMessages();
+                            $errors   = $messages;
+                        } else {
+                            $messages = array_merge($messages, $validator->getMessages());
+                            $errors   = array_merge($errors,   $validator->getErrors());
                         }
                     }
                 }
Index: tests/Zend/Form/Element/MultiCheckboxTest.php
===================================================================
--- tests/Zend/Form/Element/MultiCheckboxTest.php	(revision 24514)
+++ tests/Zend/Form/Element/MultiCheckboxTest.php	(working copy)
@@ -293,12 +293,29 @@
     
         $this->assertTrue($this->element->isValid(array('foo')));
         $this->assertTrue($this->element->isValid(array('foo','baz')));
-    
+        
         $this->element->setAllowEmpty(true);
         $this->assertTrue($this->element->isValid(array()));
-    
+
+        // Empty value + AllowEmpty=true = no error messages
+        $messages = $this->element->getMessages();
+        $this->assertEquals(0, count($messages), 'Received unexpected error message(s)');
+        
         $this->element->setAllowEmpty(false);
         $this->assertFalse($this->element->isValid(array()));
+        
+        // Empty value + AllowEmpty=false = notInArray error message
+        $messages = $this->element->getMessages();
+        $this->assertTrue(is_array($messages), 'Expected error message');
+        $this->assertArrayHasKey('notInArray', $messages, 'Expected \'notInArray\' error message');
+        
+        $this->element->setRequired(true)->setAllowEmpty(false);
+        $this->assertFalse($this->element->isValid(array()));
+        
+        // Empty value + Required=true + AllowEmpty=false = isEmpty error message
+        $messages = $this->element->getMessages();
+        $this->assertTrue(is_array($messages), 'Expected error message');
+        $this->assertArrayHasKey('isEmpty', $messages, 'Expected \'isEmpty\' error message');
     }
 }