I had the same problem on a site using the Thematic parent theme. Reinstalling WordPress did not resolve. To fix, I edited the following line from \wp-content\themes\thematic\page.php
<?php if ( get_post_custom_values('comments') ) thematic_comments_template() ?>
I simply removed the IF logic the author had in there and that fixed the problem. New code:
<?php thematic_comments_template() ?>
I’m not sure if there’s a flaw in the logic, but the page now displays the comment form based whether I check Edit Page > Discussion > Allow Comments. Hope this helps.
Dan
