Question : Excel Pivot Table "bug"?

I have an Excel pivot table that is acting very strangely in Excel 2007 - SP2.  I've never seen this before.  When I first created the pivot table, I noticed one of the entries showing up as "-5.32907E-15".  When looking at the detail, this field should have been zeros.  So, then I added another level of detail below the total.  When I expand the detail, I get a zero total, but when I collapse it, I get the above value.

Anyone seen anything like this before?

Answer : Excel Pivot Table "bug"?

For more info, you can get several good explanations here:

http://www.bing.com/search?q=excel+ieee+floating+point&src=IE-SearchBox&FORM=IE8SRC