LucidSW - 1:10 pm on Feb 29, 2012 (gmt 0)
You've fallen into the same trap as many others. What happens is not a game Google is playing. It's just the way the system works.
When you add a keyword, the system does a preliminary evaluation of your QS. The important thing to remember is, it does not yet have all the information it needs. It still needs to check your landing page for one thing to see if it complies with policies. I've heard of many an affiliate marketer for example saying the QS was initially set at 7 and 20 minutes later, see it go down to 1 because they had a bridge page or something.
If there's a default QS, it would not be 10 but rather 5 in my mind. It would go up or down depending on some immediately known factors. DeeCee is right, after the normal QS calculation, it came to the same conclusion as before and why your Qs went back to where it was.