We ran into this same problem when upgrading reports from 8.2 => 8.4. We reported it to Cognos as a bug -- Not sure if they've assigned a bug tracker id to it, but we got the impression it wasn't going to be fixed soon. (Obviously, if it exists in 8.3 and it has been carried forward to the next version, it's not a high priority.)
I'm sorry I don't have an answer at the moment on how to fix it, but I was planning to look into work arounds next week. I'll edit this post with any ideas I come up with.
UPDATE:
Not sure if this is an available feature of 8.3, but in 8.4 there is a new "No Data Contents" property for data containers (lists, blocks, etc.). Setting this value to yes creates two tabs at the top of the page, one for a page to be displayed if data is returned, and another for instances when no records are found. You can customize a message to be displayed using that second page. Pretty cool, actually, but buried in the documentation.
Hope that helps. If you still have problems, check out the Index topic "no data > specify what appears for a data container."