Melee "moving around" and facing

So, I have a question regarding the melee combat rules as stated in the Simple Actions list.

It states that:

If the model is already in BtB contact with an enemy model, it may make a Melee attack; this initiates a new Melee Combat exchange. In this latter case, the model may also move freely around the enemy model it is fighting...

 

This is reasonably straightforward and well explained I think. However, my question is this: how does the target of the melee attack respond, in terms of changing its facing. 

It would make sense to me that the target model should change facing so that the attacker is in it's ZoC, just as you would when first getting in to BtB. 

Does this allow you (the attacker) to move around to the rear of the model you were already in BtB with in order to force them to change facing, so that then you can charge them in the rear with another model?

Or alternatively, if you (attacker) bite the bullet, it then prevents your enemy (target model) from charging, as you need LoS to declare a charge.

If so: muahahaha ;).