This has evidently been confirmed by Microsoft, and there is a fix on the way.  For more on this, check this link:

http://blogs.msdn.com/excel/archive/2007/09/25/calculation-issue-update.aspx

It appears to be a display only bug, and the calculations are actually correct, but if you look down in the comments, you'll see it gets even more confusing.  Looking at the results below, this gets pretty wierd:

I know, I know, Windows Vista already has one.  But, if you miss looking at all the colorful blocks and watching the process, I have found a little tool (think it was in Windows IT Pro magazine a while back) called AusLogics Disk Defrag.  It’s free, and it gives some pretty decent reporting after the fact.