That seems the obvious reason people have mentioned, but that doesn't make sense to me. If Malone has 40% to begin with, how much does he have to worry about a takeover?
To me, financially, it looked like a protection to keep Malone from trying to buy up the remaining 11% to take over. It does make sense how that could have been negotiated.. but maybe in the original discussions, it was agreed that Malone was in it for the profits.. not to run it. And this is an insurance to keep him honest to his word.
I know it sounds very conspiracy theory.. but the other way makes less sense to me.