There's a lot of strange stuff going on with the toolbar and PR lately. Read some of the other threads in this forum and you'll see many other posts on it. Problem is, there ain't any solid answers on it that are better than 'just sit back and see what happens.'
I've noticed that disallowed pages are sometimes displaying guestimated PR. I didn't think that this was the norm, for some reason I remember these pages having a gray bar. I came across this when searching for potential link partners, a disallowed links page is displaying PR6.
One thing I overlooked in my earlier post is that -- as JDMorgan put me straight on a couple of weeks ago -- if you do not want Google to index the page you have to allow G to see the page (pull the disallow entry out of your robots.tx) and use the robots meta tag (meta name="robots" content="noindex,nofollow" or as appropriate).
This is also needed for Teoma and ?ATW? that will insist on listing any page that they know is there whether robots.txt tells them they are allowed to index it or not.