Tinkerpop & Orientdb 3: fetch "inherited" classes/labels

In orientdb I created a schema consisting of a parent class PARENT and child class CHILD. The child class inherits all the properties of the parent class.

As far as I understand classes are mapped to labels, therefore I can do:

graph.traversal().V().hasLabel(LABEL_PARENT)

However, this only returns vertices from PARENT but not from CHILD. How can I fetch both?

btw. SELECT FROM PARENT in fact returns both, but I want to use tinkerpop.

Update: I tried the following, but it gives me the CHILD vertex twice:
graph.traversal().V().hasLabel(LABEL_PARENT,LABEL_CHILD)