Index: library/Zend/Form/Element.php
===================================================================
--- library/Zend/Form/Element.php	(revision 18081)
+++ library/Zend/Form/Element.php	(working copy)
@@ -2099,7 +2099,7 @@
             if (null !== $translator) {
                 $message = $translator->translate($message);
             }
-            if ($this->isArray() || is_array($value)) {
+            if ($this->isArray() && is_array($value)) {
                 $aggregateMessages = array();
                 foreach ($value as $val) {
                     $aggregateMessages[] = str_replace('%value%', $val, $message);
Index: tests/Zend/Form/Element/MultiCheckboxTest.php
===================================================================
--- tests/Zend/Form/Element/MultiCheckboxTest.php	(revision 18081)
+++ tests/Zend/Form/Element/MultiCheckboxTest.php	(working copy)
@@ -263,6 +263,22 @@
         $this->assertFalse($this->element->isValid('test'));
     }
     /**#@-*/
+    
+    /**
+     * @see ZF-5412
+     */
+    public function testAddingError()
+    {
+        $options = array(
+            'foo' => 'Foo Value',
+            'bar' => 'Bar Value',
+            'baz' => 'Baz Value',
+        );
+        $this->element->setMultiOptions($options);
+        $this->element->addError('someError');
+        $this->assertTrue($this->element->hasErrors());
+        $this->assertEquals(array('someError'), $this->element->getErrorMessages());
+    }
 }
 
 // Call Zend_Form_Element_MultiCheckboxTest::main() if this source file is executed directly.