Currently cleave (and great cleave, and supreme cleave) behaves differently with quarterstaff than with other thf weapons, (greatsword, greataxe, greatclub, maul, bastard sword with shield, dwarven axe with shield, etc) in that quarterstaff cleaves don't proc glancing blows as they should.
This has been a problem for over a year and has significant impact on some (acrobat) builds that do a lot of cleaving.