It might have already crossed your mind, but procs are independent of the number of swings. Proc rate depends on which hand a weapon is in (secondary lower proc rate than primary), the proc rate of the weapon in question (some have different proc rates, and your dex (guess this applies to pets as well, but stats and pets are different from stats and pc's)
Basically even if for some reason swings are set to zero for the offhand or disabled, if there is a flag of some sort for that slot for a proc, it wouldn't be surprising to see it fire.
All in how it is coded.
|