Tested retard and it added timing ???

Using msd digital retard 8975 which is hooked up to my nitrous solenoids which is controlled by my edelbrock nitrous controller. Brought rpms up with timing light on, hit micro switch for nitrous and it actually added the amount of timing I had on dials on msd How is this possible? I hooked up other 2 stages of retard to a relay that removes ground by, which is powered by my controller and it works perfect