either we inherit it from the parent or set it explicitly: 
https://github.com/doctrine/phpcr-odm/blob/master/lib/Doctrine/ODM/PHPCR/Mapping/ClassMetadata.php#L1235

the code is relying on that in a couple of places alreay.

but then again, it seems my local phpunit sometimes does not detect this issue. but travis should show it, right?