Basically, a representative who splits the network by commiting two conflicting votes is (AIUI) by definition defective, and any representative that observes bo

Basically, a representative who splits the network by commiting two conflicting votes is (AIUI) by definition defective, and any representative that observes both potential blocks knows that, and can propagate that knowledge to any representative it communicates with (which must be most of them in order for them know what that (observing) representative's vote was). And once most representatives know that a vote was spoiled, they can throw it out (along with the two blocks it distiguishes between, although I think those still need to stored, just the transactions in them are treated as not having happened). But, as I said, I'm not sure about the logistics/provable-correctness of making sure that the half of the network that voted one way and the half that voted the other way always have a chance to compare notes soon enough to catch a spoiled vote.