I had several perfect hub scores, then made minor corrections, mostly grammatical and the scores dropped into the 80's. They are slowly climbing back out of the trenches, but I really don't understand the drop. One was top ten hub of the day on the last Grow The Hub Pot Challenge, so I don't think it sucked...lol.
As a result, I can't take the scores too seriously.
I didn't even know there was a Panda update in May! Guess I got lucky this time...however, in the past, I was badly hit three different times...so I know how you feel! Doing well right now, but as we all know, that could change tomorrow!