After fighting a cebolla, it seems that the attack power down does indeed wear off if other attack power modifying effects wear off once it has been applied. I'm not sure myself what's causing the issue, but this information should be enough for the devs to figure it out.
This game is just full of glitches. The attack power down from unihound's light beam stacks until your opponent's attacks all deal single-digit damage, and it doesn't wear off for the entire fight.
"based on my calculations from your monster's data and mine, I've predicted there's 70% I'll win, so lets fight!"
Either your calculations are way off the mark, or you didn't use the data from my LEVEL 30 MAXED OUT UNIHOUND.