Help me out where would I find the changes to this trick. As far as I can tell with both phb and dmg open in front of me I can't find any restriction on when one can use cleave. I can understand the swarm changes but I dont see anything else. Cleave can only be used once per round (phb92) and great cleave is unlimited per round. (phb 94). Doesn't cleave represnt a continuation of the same swing. (ala 7 flies with one blow?) A cleave would be part of the single attack provided by the AOO then and as long as one had the appropriate feat and the aoo dropped the target everything looks ok.
To the arguement that my guard is still up and my mage friend casts a spell provoking an AOO so I cant be cleaved: My guard is not propbaly expecting a great axe comming through where magic-man was standing nor would it be as steadfast as normal considering said axe just dropped my comrade.
Cleave I think works because the blow was strong enough (str prereq) to tear through the target and continue on to attack the next one. (go conan go!) or by monk through such finesse that they are able to set up combinations.(dont need the str prereq) In either case the fact that a cleave attack is a free action means it is part of the action used to initate it and one should be awarded the cleave even on AOO. Best not put the mage in the front line... he'll probably do more harm than good.
Of course if there is specific rulling in print to the contrary Ill notify Hurok right away!