Curious archive problem?

Not a major problem to be sure, but one that has me totally baffled. I started my blog in April 2007. I have no idea when this first occurred because frankly I pay little attention to the archive listing, but the date of the first archive says “April 1300”, followed by “May 2007”.

I have no idea at all how to “fix” this, or if indeed it’s worth the bother, but it has me scratching my head how it could happen.

Any ideas?