David,
I can't duplicate your issue, can you post the query and rdl? I'm attaching an example I put together that I think matches your scenario, but I'm not seeing the issue with what I have setup.
Jack Corbett
Consultant - Straight Path Solutions
Check out these links on how to get faster and more accurate answers:
Forum Etiquette: How to post data/code on a forum to get the best help
Need an Answer? Actually, No ... You Need a Question