TIMESTAMPDIFF function when filtered doesnt give proper results

Hi,

I have a requirement to show only those records which were created in the last 12 months from current month. For this i used TIMESTAMPDIFF function with (month parameter,created date,current date). I found that in the table view, the results are shown correctly (numerical values for TIMESTAMPDIFF). For example, current month is June - so for a June 2011 record the difference evaluates to 12 and for a May 2011 record the difference evaluates to 13. Now if i put a filter on this difference and restrict it to <= 12, i can see that some of the records of May