diff --git a/lib/Doctrine/ORM/UnitOfWork.php b/lib/Doctrine/ORM/UnitOfWork.php
index 684210272..d62eb62c7 100644
--- a/lib/Doctrine/ORM/UnitOfWork.php
+++ b/lib/Doctrine/ORM/UnitOfWork.php
@@ -1456,7 +1456,8 @@ class UnitOfWork implements PropertyChangedListener
                         }
                         if ($assoc2['isCascadeMerge']) {
                             $managedCol->initialize();
-                            if (!$managedCol->isEmpty()) {
+                            // clear and set dirty a managed collection if its not also the same collection to merge from.
+                            if (!$managedCol->isEmpty() && $managedCol != $mergeCol) {
                                 $managedCol->unwrap()->clear();
                                 $managedCol->setDirty(true);
                                 if ($assoc2['isOwningSide'] && $assoc2['type'] == ClassMetadata::MANY_TO_MANY && $class->isChangeTrackingNotify()) {
@@ -1655,6 +1656,10 @@ class UnitOfWork implements PropertyChangedListener
             }
             $relatedEntities = $class->reflFields[$assoc['fieldName']]->getValue($entity);
             if ($relatedEntities instanceof Collection) {
+                if ($relatedEntities === $class->reflFields[$assoc['fieldName']]->getValue($managedCopy)) {
+                    continue;
+                }
+
                 if ($relatedEntities instanceof PersistentCollection) {
                     // Unwrap so that foreach() does not initialize
                     $relatedEntities = $relatedEntities->unwrap();
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC1276Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC1276Test.php
new file mode 100644
index 000000000..1b9dc8c99
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/DDC1276Test.php
@@ -0,0 +1,50 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Common\Collections\ArrayCollection;
+use Doctrine\Tests\Models\CMS\CmsUser;
+use Doctrine\Tests\Models\CMS\CmsGroup;
+
+require_once __DIR__ . '/../../../TestInit.php';
+
+/**
+ * @group DDC-1276
+ */
+class DDC1276Test extends \Doctrine\Tests\OrmFunctionalTestCase
+{
+    public function setUp()
+    {
+        $this->useModelSet('cms');
+        parent::setUp();
+    }
+
+    public function testIssue()
+    {
+        $user = new CmsUser();
+        $user->name = "Benjamin";
+        $user->username = "beberlei";
+        $user->status = "active";
+        $this->_em->persist($user);
+
+        for ($i = 0; $i < 2; $i++) {
+            $group = new CmsGroup();
+            $group->name = "group".$i;
+            $user->groups[] = $group;
+            $this->_em->persist($group);
+        }
+        $this->_em->flush();
+        $this->_em->clear();
+
+        $user = $this->_em->find('Doctrine\Tests\Models\CMS\CmsUser', $user->id);
+        $cloned = clone $user;
+        
+        $this->assertSame($user->groups, $cloned->groups);
+        $this->assertEquals(2, count($user->groups));
+        $this->_em->merge($cloned);
+
+        $this->assertEquals(2, count($user->groups));
+
+        $this->_em->flush();
+    }
+}
\ No newline at end of file