Actually, it's a bug in your HTML (although you did confuse me for a few minutes...)
The attribute you're looking for is bgcolor;  background loads a background image, and expects a URL argument.  When you feed it with #FFFFFF, it tries to access
http://www.dukemarket.com/bug.php#FFFFFF to load it as a background image, access the page again, and causes a second insert.

It was a good challenge though :)

although the link is dead, from zeev's response one can 
gather that gkm had a script that was double inserting into 
a db because he mistakenly put a color code in the 
background tag.

this serves as a good warning not to have a misformed 
background attribute in your body tag. i found that just an 
empty background attribute (background="") caused a script 
to run twice (maybe calling itself?). this caused db 
operations to be performed twice.

Wow wow , guy you just made me fly again (lol)...
My Mysql_query was acting weird, inserting double records in my table :) ....
i was stuck because of this f*** error in my html code and i've lost 1 day searching over the internet to understand what was wrong , looking around because i just re-installed my apache/mysql server (abria MERLIN) and noticed that bug.

Thx a lot for this :)

Stef ( France) - www.e-planete.com