So far there's been no real buzz about this, leading me to believe that either Fox is officially releasing episodes perhaps through it's own site earlier than it airs it. Or judging by the video, it appears that British channel Sky 1 may have goofed and aired the episode days earlier than expected.
Either way here's peak at the episode:
next week's episode: Wedding for Disaster, details how Marge and Homer realize they're not actually married and end up re-pledging their vows of marriage to make it official. The episode starts with the Simpsons family going to a field and gardening expo having being duped by Marge.
Update: ok it turns out it wasn't leaked, but rather Sky 1 Ireland had the rights from Fox to broadcast it several days early (world premier exclusive) on St. Patricks Day (Tuesday March 18th)