[@so1o Participant 18 years, 1 month ago]

in function post_form –

$page == get_page_number( $topic->topic_posts + $add )

this is probably being evaluated as false.

i say this because this your paging is messed up..

http://booksinbed.com/wordpress/bbpress/topic.php?id=3&page=2

if you go to the above link the number 1 should have link in the page navigation. in your case page 2 has..

debug the get_page_number function whats getting loose..