EJB-QL query never returning unless another query is run

Question

I have a strange strange problem.

When executing the following EJB-QL query, my ENTIRE application will stop responding to requests, as the query never finishes executing.

Query q = em.createQuery("SELECT o from RoomReservation as o WHERE o.deleted = FALSE AND o.room.id IN (Select r.id from Room as r where r.deleted = FALSE AND r.type.name = 'CLASSROOM')");

However, if I execute this query before I execute the other query, it runs without issue.

Query dumbQuery = em.createQuery("SELECT o from Room as o WHERE o.deleted = FALSE");

Any idea what in the world is going on?