Well, when you're inside Monster Carnival PQ you can't use any potions, including attack potions. This is intentional and is supposed to be a part of the PQ. However, there is a way to enter the PQ with an attack potion active, by using it before entering the PQ, at the lobby - where people do the party recruiting. So if you use the attack potion then, and enter the PQ quickly, you get to keep the attack boost effects of the potion while inside the PQ. That, as far as I am aware, is not supposed to happen. Or, it's not supposed to be possible, I guess. Maybe the advantage is not big, but it's not supposed to be like that, since you're not supposed to have any potions on in this PQ. I'm not sure if you can call this a bug but it's still a problem.
This has always been a thing even in the live servers. There honestly is no downside to this, using Wa pots enables people to kill monsters faster and Gain more exp. Heck one might even apple inside for shits and giggles
