The JTR / Sion taunt thing is one of those weird situations where he's, by rule, taunting at the start of her turn and before she removes the debuffs. The sequence goes. It's her turn (she has debuffs), Sion taunts, she dispels debuffs. I.e., at the start of her turn she still has debuffs so he still taunts.
Same mechanic applies to Visas when facing sith. She's attacked, she counters, she gains debuff, she cleanses debuff.
It's just one of those weird order of operation things.