When we switched over from vBulletin to our own unique platform back in March 2012, one of the things that changed was the way that post quality score was calculated. Most members noticed their quality score had suddenly changed by a few points.
Since then, however, over the past year and a half, there have already been two separate instances of members complaining that an ill-willed member went on a downvoting spree with the sole intention of being malicious and affecting their quality score.
Our original formula for calculating post quality score was much better at softening the effects of this type of malice, and therefore I've decided to revert to the previous calculation.
Once again, you'll notice a change in your quality score today. I apologize for the confusion.