PivotTables in Excel 2004 calculate incorrect standard deviations
 

I've recently upgraded from Excel X for Mac to Excel 2004. Everything
(almost) seems to be working fine but I've come across a problem with
PivotTables. I have a data set which I want to summarize with a PivotTable.
The PivotTable simply calculates averages, standard deviations and the number
of values in each group. I've also calculated these statistics using Excel's
built-in functions and from 'first principles'. The calculated values for the
average using each method are identical but the standard deviation calculated
with the PivotTable is way off (eg 0.1623 instead of 1.1418). Interestingly,
if I open the spreadsheet in Excel X for Mac or any version of Excel on a PC
(including Excel 2003), all the calculations are correct.

Any suggestions?