Ingo,
I was finally able to get back to this problem. I used the same Bex query to create a Webi from the BI Launch Pad. When run from the Launch Pad, the date parameters were displayed as expected.
The suggestion was made that there is something wrong with the installation of the Webi Rich Client on my PC. We will be moving to a more recent service pack soon, so I will wait until then to attempt to update my Rich Client.
I do appreciate all the input I received.
Thanks everyone,
Ron