Deleting a ProcessInstance having a running Sub-ProcessInstance fails

When trying to delete a ProcessInstance using ExecutionService.deleteProcessInstance() an SQLException is thrown if the ProcessInstance has a running Sub-ProcessInstance.
Trying to delete the Sub-ProcessInstance first doesn't work either.
The problem here are the foreign key constraints:

Deleting the super process:
org.postgresql.util.PSQLException: ERROR: update or delete on table "jbpm4_execution" violates foreign key constraint "fk_exec_superexec" on table "jbpm4_execution"
Detail: Key (dbid_)=(176) is still referenced from table "jbpm4_execution".

Deleting the sub process:
org.postgresql.util.PSQLException: ERROR: update or delete on table "jbpm4_execution" violates foreign key constraint "fk_exec_subpi" on table "jbpm4_execution"
Detail: Key (dbid_)=(179) is still referenced from table "jbpm4_execution".

Maybe loosen up the sub>super constraint?