Hmmm… I upgraded to WP 2.0.5 today (yes I know I’m late) and it appears to have marked some old posts as new. Hence they may well appear in the Dashboard.
I haven’t done anything to prompt this other than upgrade. I’m not sure what has caused this, but I think one or two other people had similar problems. Sorry for the confusion.
Update: I just thought of something I did change.
I changed the blog description: I changed “not quite so daily thoughts” to be “not-quite-so-daily thoughts”. I wonder whether that is enough to trigger the problem with the software at WordPress Planet?