I found an issue where the new lucky pants damage boost perk will trigger upon damaging enemies with other hand cannons but not with Vulpeca. I am not sure what exact property it is that causes this issue but I am certain that it is not related to any particular weapon perks and related to the weapon itself. Perhaps it is Stasis? More details: The "Illegally modded holster" perk does appear as well as the "out of luck" debuff. It is only the damage boost that does not seem to apply.