Core

Since TYPO3 6.2.10 the class resolving from old namespace way with underscores seems to not work with the object manager/object container anymore. This can lead to very strange problems, because the object manager instantiates singleton classes maybe twice.

Example:

$persistenceManager1 = $this->objectManager->get('TYPO3\CMS\Extbase\Persistence\Generic\PersistenceManagerInterface');
$persistenceManager2 = $this->objectManager->get('Tx_Extbase_Persistence_ManagerInterface');

// Since TYPO3 6.2.10 results in different hash values, because they are two different instances
var_dump(spl_object_hash($persistenceManager1));
var_dump(spl_object_hash($persistenceManager2));

// Thus since TYPO3 6.2.10 following comparison returns FALSE 
var_dump($persistenceManager1 === $persistenceManager2);

// Same behavior with another example class (here with object manager) 
$objectManager1 = $this->objectManager->get('Tx_Extbase_Object_ObjectManagerInterface');
$objectManager2 = $this->objectManager->get('TYPO3\CMS\Extbase\Object\ObjectManagerInterface');

var_dump(spl_object_hash($objectManager1));
var_dump(spl_object_hash($objectManager2));

var_dump($objectManager1 === $objectManager2); // Returns FALSE

Best regards,
Rob