Mount and rider attacks of Opportunity?

[ShadowsGrnEyes]

Situation: The mount moves away from a threatened square in a manner that provokes attacks of opportunity. The mount uses acrobatics to avoid the attacks and succeeds on the acrobatics roll. The attacks have been avoided.

Questions: Must the rider make their own Acrobatics or has the mount evaded the attacks for both of them as a rider is essentially a "backpack"?
Can the rider make their own acrobatics check to avoid the attacks?
Is the rider forced to take the attacks and unable to avoid because they are on the mount even if the mount avoids the attacks?

If there is a ruling on this in the rules I would like a reference to show the group as it became a small debate and we could not find the solution clearly defined.

[Ssalarn]

This one is in a bit of a gray area in the rules, but the way we've always played it is that the enemy can choose whether to direct his AoO at the mount or rider. The mount is spending it's action to move, so it's the one that provoked, but we let the attacker choose whom to direct his AoO at due to the weird symbiosis of mount and rider. The big thing is that there is only one provoking action, so the enemy only gets one AoO.

[Yanisa]

There is nothing in the rules about it as far as I can see (See Mounted Combat (http://www.d20pfsrd.com/gamemastering/combat#TOC-Mounted-Combat) and Ride (http://www.d20pfsrd.com/skills/ride)). Then again the rider doesn't move (take an move action), only the mount does, so only the mount provokes an attack of opportunity, the rider is safe. But that is common sense rather then something hard in the RAW.