I mean, it can't be that hard to put a turn timer on it, JKA's unique offense bonus expires after "Perform Move"
They can probably just add that same feature to Chopper as he only taunts for 1 turn anyways, so once he "Performs Move" the next turn that 1 turn will be over and the evasion bonus should go away if he hadn't had buff immunity/shock in the first place.
Or they could actually make the evasion bonus effect only be applied if he actually has the taunt buff active, which should be possible if they can make sith immune to critical hits while they have a stealth buff under a zeta maul lead. Which would also be a fix for STH as well. I could be wrong, but that could potentially fix things by using the same kind of code they have for other characters. Even if those are built into leader abilities it could work elsewhere right?
