Have you verified that the chart figures you see for last November are not infact for this November? I'm wondering that if you are not grouping on Years & Months (two levels in the Category fields in the chart) it might not be sorting them correctly. The query is run against the server by SSRS so there is no reason you would get a different result.

Looking at your query, I dont think it works. Are you not getting an "is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause." error?