[bbDev] Permalinks Plugin - Changing Mod Rewrite Rules

[info at swing-sets.us]

Hello,
I am trying to change the bbPress permalinks but I am stuck when it  
comes to paggination. I've already written a plugin and I have a  
working example at www.dfur.com

My permalinks structure idea is
www.example.com/forum_name
www.example.com/forum_name/page/2 for pagination
www.example.com/forum_name/topic_id
www.example.com/forum_name/topic_id/page/2 for pagination

Pagination can be change from page/2 to page_2, same thing with the topic_id.

There are 2 reasons for witch I am working on this:
1. www.example.com/forum_name/topic_id will offer better usability and  
help with the search engine rankings
2. A custom permalink structure will allow other platform forums  
owners to switch to bbPress AND keep their current linking structure.  
I have a PHPBB forum that I want to move to bbPress but if I will  
loose all the links there will be a nightmare restoring all my rakings.

I?ve written a plugin that changes the forum links to  
www.example.com/forum_name.
You can see a working example on my test site www.dfur.com, the plugin  
can be downloaded from http://bbpress.org/forums/topic/771
To make this work I?ve added in to following link for each topic of my  
site in htaccess
RewriteRule ^designer_furniture/topic([0-9]+)$ /topic.php?id=$1 [L,QSA]

The problem comes to pagination. Please see  
http://www.dfur.com/designer_furniture
The ?page 2? pagination should be  
http://www.dfur.com/designer_furniture/page/2 However this link does  
not works. The 301 from bb_repermalink function in  
bb-includes/functions.php redirect me back to the forum category.

 From what I?ve understood the bb_repermalink makes a check to see if  
the links is correctly created: if - ( is_forum() )? $permalink =  
get_forum_link( $permalink, $page ); and if this fails it gives the  
301 redirect.
 From my point of view creating a 301 (permanently moved) is not a  
good move for search engines, especially Google. The 301 may cause a  
duplicate page issue with Google. The standard recommendation for a  
non existing page is a 404 with a noindex, nofollow. I see that the  
wordpress and bbpress forums have the 404 but the regular bbpress  
powered forums do not have this option.

Anyway I need some help finishing this plugin. Why am I being  
redirected and how can I avoid that? How can I bypass this 301 and  
what triggers it?

Thank you,
Mircea Piturca.