On November 11, Massachusetts Governor Duval Patrick signed HB 3788, which moves the non-presidential primary from September 18 to September 6. This makes it possible for Massachusetts to comply (just barely) with the 2009 federal law that requires overseas absentee ballots to be mailed at least 45 days before any federal primary or federal general election. There could still be a problem if there are any primary contests that are so close that it takes an extra long time to determine the primary winner.
September 6 is a Thursday, not a Tuesday. The state did not want to hold an election on the day after a federal holiday. The primary date change has no effect on the petition deadline for independent candidates and the nominees of unqualified parties.
The fact that HB 3788 has been signed reduces the chances that the legislature will pass the bill that combines the March presidential primary and the September non-presidential primary into a unified primary in June, even though that idea would save at least $8,000,000. Thanks to Josh Putnam of Frontloading HQ for this news.