SHA256 guarantees that no two tickets will have the same hash.
That's not true. There's no guarantee that SHA256 doesn't generate the same output for two different inputs. In fact in general it's guaranteed that there are collisions in any hash function, since the input space is infinite and the output space is finite. In practice of course it's incredibly unlikely that you'll ever have two tickets with the same hash.
Right, a miner who plays more than 50 coin worth is incentivised to throw out a losing hash
If he's mining in a pool, he doesn't need to have anything like 50 coins worth of lottery tickets, since the block he throws away won't cost him very much at all.
Gah, thx, how have I never thought of that.
Odd effect. If games dependent on the hash of blocks become popular it could actually start to hurt pools. Hurts bigger pools more than smaller because what you give up is something like your power/pool power times reward.
Player-miners would just need a little but of code to let them set rejection criteria and then start cashing in their teeny edge.