See test.jpa.general RelationshipsTest where there is a test with @EmbeddedId and with the owning class also having a join table 1-N relation. When the persist is attempted it tries to insert into the join table with null for the owner PK fields. The problem is likely the internally selected objectId class (ObjectIdentity) which doesn't allow for fields that are persistable in their own right. The workaround would be for the user to define their own @IdClass.