VERY Weird Problem

[hobbybox]

I created a user profile field that asks members for a URL to a home page....

To show this field in the post bit I use the following code

<if condition="$post['field9']"><div><b>Trade Page:</b> <a href="$post[field9]" target="_blank">Visit My Page</a></div></if>

Field9 represents what they input. The wierd problem is this..

if a member puts http://sitename.com all works great - the 'Visit My Page' is linked to the URL they input HOWEVER if they leave off the http:// and put say www.sitename.com vbulletin for some reason adds our domain http://oursite.com/forums/ then puts the field9

end result for the link is http://oursite.com/forums/www.sitename.com

Why in the world would vbulletin add our forum url to this field? Any ideas