I have a Pivot Table that looks as follows:

2009 2008
Data Feb Jan Dec
Revenue 5,000,000.00 3,282,739.72 4,329,509.90
% Difference 52.31% 20.37%

The row labled % Difference is the percentage difference in revenue between
months. The data for dates shown is grouped by month and by year. The %
Difference row was derived by selecting Pivot Table Field, Options, Show Data
As, % Difference From, Date, Next.

For some reason the January 2009 amount is not being calculated. The answer
should be 24.17%. Can anyone shed any light here? Does it have something to
do with the way yhings are being grouped?