I just tried this on two new installations (Fedora 9 and Ubuntu 8.04) using the same version of hardcopy.pm that you are using. The installations were done with version rel-2-4-patches following the instructions at http://webwork.maa.org/wiki/Installation_Manual_for_2.4#Installation_instructions_for_specific_operating_systems .
First I changed the due and answer dates of set 0 from 2009 to 2008 and then I logged in as a regular student (jsmith) and downloaded a hard copy with answers. And the answers were there.
I have no idea what the problem might be. I assume you haven't changed any of the default permissionLevels in global.conf and double checked that the answer date has actually passed for the student in question. The fact that you can get the answers when acting as a student seems to indicate that there is either a problem with how dates are being processed or with permission levels. It's probably something very simple but I can't think of what it would be.