On December 19, a lawsuit was filed in the Montana Supreme Court to remove the ballot measures that would establish a top-two system in Montana, and repeal election-day voter registration. See this story. Thanks to Mike Fellows for the link.
The top-two measure is on the ballot because the Republican majority in the legislature placed it on the ballot. The sponsor of the bill for top-two is quoted as saying that he has a problem with elections in which the winner does not receive a majority of the vote. He seems not to have read about the California U.S. House election in 2012 in the 31st district. Two Republicans were the only candidates on the ballot in November, even though the district is strongly Democratic. So 23.1% of the voters who cast a ballot left U.S. House blank. Therefore, the winner, Congressman Gary Miller, did not get a majority of the people who cast a ballot.