This happened for a bit in Beta...what you want to do every time you reach an achievement or get / do something significant if you are afraid of a roll back, just log out and log back in or zone (ie trigger a loading screen). This way if you roll back you go back as far as your last load. This weekend we had one but I had just exited a solo dungeon before it happened. While some guild mates lost 20 minutes worth of progression (ended up back in 4 man dungeons etc)...I lost maybe less than a minute of riding my horse towards a wayshrine.