This is unsupported by anything in the rules.Grayhawk said:'An attack of opportunity is caused by a situation where one of the combatants puts themselves into a position of vulnerability. Since this is a free attack and there would be no penalty for doing nothing, making a sunder attack as an attack of opportunity does not provoke an attack of opportunity.'
Worse, it doesn't even appear to make sense. What the heck does he mean by "no penalty for doing nothing"? There's never a penalty for giving up an action! If I were to spend a turn twiddling my thumbs, nothing bad would happen to me, but if I used that turn to sunder I'd still suffer an AoO.
I wonder why Customer Service doesn't require their employees to read the rulebook.