I saw a jump in quality score too. If it isn't a bug, then it is a flawed concept unless they are trying to mess with automated bid algorithms. The problem is that when QS jumps to 10, the first page bid estimates go down to next to nothing. If you are using first page bid estimates as a baseline with your automated bid algorithm, then your software will crank your bid down to prevent overpaying. But, because the true FPB estimate is still very high, you no longer get impressions.
On a possibly related note, my first page bid estimates are no longer moving in .05 cent intervals. My first page bid increments used to be .01 - .09, .1, .15, .2, .25 etc. Now they "appear" to be in one cent increments across the board. Has anyone else seen this?