I didn't wrote my thoughts on this beforehand, as to not sway the option in any direction. I thought about your point before, but this reasoning is only rooted in an "oxfordian" Interpretation that 'must' trumps 'may', which isn't necessary true within the game mechanics and can have wider implications
(for example, if 'must' compells the model to take the melee action than it has to pay any associated cost and use any enableing ability, if the attack is otherwise impossible, whenever it has the chance. Like discarding a card, if challenged; Using an ice pillar as point of origin [Rasputina, Cold Snap], if otherwise out of range; Discarding Power tokens to futher reach if necessary with welding torch; and so on).
As 'bring it' doesn't change control of the model, i would tend to argue, it doesn't force the controler to chose in a specific way for any subsequent options (as obey would do). I thought there was a FAQ regarding forced choices, but i am unable to find it again.
In my Opinion this boils down to
A) "Must" overrules the controler-decides rulesset (p.26)
B) "Must" doesn't
I favor B only to not open the can of worms A would bring.