empty categories returning 404 (WP2.1)

Hi

I’m using WordPress 2.1 with “Date and name based” permalinks. It all seems to be working fine, except that categories with no posts display the “404 Not Found” page, rather than the “Not Found with search form” that the archive page is supposed to display when a category is empty. Note that it worked fine -before- changing the permalink structure.

Is anyone else experiencing this problem and are there any workarounds? I’ve seen similar issues with older versions of WP, but nothing recent.