As far as I know, the bull elephants have some kind of hormonal change that makes them act crazy. It's like PMS or sorts for them. Saw it on National Geographic... Can't remember the exact term for it though...
Don't they say they are in 'musk'. You're right, the surge of hormones, or testosterone or whatever sends them crazy.
Poor elephants. They haven't got anywhere to go and they get beaten and used by these people.