I noticed that when I disable Topic Tags from the bbPress settings menu, that it will remove the attachment fields aswell.
Problem is with the hook that is being used to output your form. Simple solution would be to use a different hook, which can not be disabled from the bbpress settings.
Great plugin btw!
code/attachments/front.php line 33/34:
add_action('bbp_theme_after_reply_form_tags', array(&$this, 'embed_form'));
add_action('bbp_theme_after_topic_form_tags', array(&$this, 'embed_form'));
