pivot table date problem

OK,

group the date field thus:

Starting at: 1-Aug-2009
Ending at: 31-Jul-2010

Select Month in the "By" list.

Now filter by date. You will see tick boxes for the months, but you will also see tickboxes for "<01/08/2009" and ">31/07/2010". Unselect the latter two from the filter and you will see only data for the last year.

see attached.