The regulator creep from the flatline would make it more reactive and hard to control. You would be able to feel the increase in trigger kick if that happened. If you are not really noticing any increase in trigger kick back, but do notice it going full auto or firing on the pull and release, it is probably a timing issue where the on-off is releasing air before the sear can rotate far enough to lock the bolt in the reset position. That doesn't mean the on-off is bad or even the on-off orings are bad.
There are typically three things linked to timing of an automag. The sear/bolt interaction, the sear/on-off interaction, and the on-off length.
If the regulator on the flatline is creeping, it may be more noticeable as the air pressure gets lower in the tank. The orings don't seal as well at lower pressures, especially if they have a blemish in them.
Except for the Automag in front, its usually the man behind the equipment that counts.