Clean URLS With Mod (ISAPI) Rewrite

After much trial and error we have achieved, what we think, are appropriate URL rewrites.

Notice this URL:
http://www.rentittoday.com/charter-jets-and-helicopters/Charter-Jet-Rentals-Stratos-Challenger-604-9?Charter-Jet-Rentals-Stratos-Challenger-604-9

And notice how it repeats the listing twice.
?Charter-Jet-Rentals-Stratos-Challenger-604-9

However the appropriate URL that we are trying to achieve in the end still works!

http://www.rentittoday.com/charter-jets-and-helicopters/Charter-Jet-Rentals-Stratos-Challenger-604-9

We're trying to figure out if it's appending the listing twice because of our htaccess code or something within CMS (such as viewer url, filename fields, or some other code)

The htaccess code for the above string is this:

RewriteBase /
RewriteCond %{QUERY_STRING} (.*)

RewriteRule ^viewers/air_plane_charter_jets_details\.php$ /charter-jets-and-helicopters/%1 [NC,R=301]

RewriteRule ^charter-jets-and-helicopters/([^/.]+)/?$ /viewers/air_plane_charter_jets_details.php?$1 [NC,L]