page refresh problem

[Desperado]

Hi,

I have 2 value prompts month and year in my report. When i click on back button in my IE from cognos viewer and after selecting different month and year , the report is showing both the values. like , Assume that i selected May 2007 for the first time and after that if i cclick on back button and select April 2006 then it's showing as Apr, May in month and 2006,2007 in year. how do i solve this problem ???
thanks in Advance