Currently, when a MUX instance is marked as mmi_tune_failed, it is not being reset. Because of this, after editing the MUX and correcting its parameters, the MUX cannot be used anymore unless the system is restarted. This issue is addressed by setting mmi->mmi_tune_failed to 0 whenever the MUX is saved.
This can be easily reproduced by setting an out-of-range frequency on any Linux DVB tuner and then trying to play with the MUX settings.