Crash when trying to delete a duplicated song

Traceback (most recent call last):
  File "/home/samuel/programming/openlp/trunk/openlp/plugins/songs/lib/mediaitem.py", line 374, in on_delete_click
    delete_song(item_id, self.plugin)
  File "/home/samuel/programming/openlp/trunk/openlp/plugins/songs/lib/__init__.py", line 551, in delete_song
    song_plugin.manager.delete_object(Song, song_id)
  File "/home/samuel/programming/openlp/trunk/openlp/core/lib/db.py", line 372, in delete_object
    self.session.commit()
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/scoping.py", line 149, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/session.py", line 765, in commit
    self.transaction.commit()
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/session.py", line 370, in commit
    self._prepare_impl()
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/session.py", line 350, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/session.py", line 1879, in flush
    self._flush(objects)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/session.py", line 1997, in _flush
    transaction.rollback(_capture_exception=True)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/util/langhelpers.py", line 57, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/util/compat.py", line 168, in reraise
    raise value
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/session.py", line 1961, in _flush
    flush_context.execute()
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/unitofwork.py", line 370, in execute
    rec.execute(self)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/unitofwork.py", line 477, in execute
    self.dependency_processor.process_deletes(uow, states)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/dependency.py", line 1016, in process_deletes
    secondary_update, secondary_delete)
  File "/usr/local/lib/python3.4/dist-packages/sqlalchemy/orm/dependency.py", line 1104, in _run_crud
    result.rowcount)
sqlalchemy.orm.exc.StaleDataError: DELETE statement on table 'authors_songs' expected to delete 4 row(s); Only 5 were matched.