[MultiWonder]

Weapons Used: Fuuma (Potential Skill worth nothing: Wear Down)
Move Used: Double Down
Issue: Hitting an opponent with maximum Wear Down stacks (20) with Double Down will reset the stacks regardless of rounds left.  (In Double Down's case, LV 5)

Replicating this bug is fairly simple.  Take any weapon with the Wear Down shared potential and hit an enemy until they reach the maximum amount of LV for Wear Down (LV 20).  Upon hitting them with Double Down (the only skill I'm aware of that applies wear down at the moment, but I'm pretty sure other skills that apply wear down do the same thing in this case), all of these stacks will go away, only to be reapplied once more and effectively resetting the stacks.

On a slightly related note!
This seems to apply to some charm effects too, though I may just make a separate post regarding this (since I'd have to do a little more studying on how those in particular work)