In the following sequence of code, the QCM/QOM::error() function can return incorrect information:

manager->save(good objects)
 -> contactsAdded etc signal
  -> slot { manager->causeError(); }
 -> manager engine save returns
manager->error() == error from causeError(), rather than NoError.

It's even more complicated if the engine itself uses the error within the save function (e.g. return *error == NoError;)