You'd think that. It was like that in 2005 but for 2008 I find that unless I change a parameter the result set stays cached. I even have a shortcutted batch file that deletes all the .rdl.data files. I got tired of banging my head and never seeing changes so I just force the issue now.

I've looked online for a solution too. I never did find one(That being said I didn't look too hard).