Addon domains's subdirectory keeps getting redirected?

[Xumedia]

For the sake of making it easier, I made the domain names generic. Here's the problem...

I have a website, website.com
I have an addon domain, addon.com

addon.com is hosted on addon.website.com
then I have a forum in addon.com, which would be addon.com/forum or addon.website.com/forum

Now when outside websites link to addon.com/forum, the link always gets redirected to the longer URL, addon.website.com/forum which is very annoying.

Does anyone know why it does this and how I can fix it?

Note: I've checked all my .htaccess files and its not that... I'm very confused.

[shigmy]

Has this question been answered in another thread or does someone know what he's talking about? I seem to be having the same problem.

I can access files directly without it redirecting the address in the browser.

Example:
"www.addon.com/file.html" OR "www.addon.com/images/file.jpg" will stay just like that in the browser address bar and access the file just fine.

But entering directories such as
"www.addon.com/images/" get redirected in the browser address to "www.addon.domain.com/images/".

The folders are still there and everything looks correct. All except for the address.

[shigmy]

Found it:

http://helpdesk.bluehost.com/kb/index.php?x=&mod_id=2&id=152

[aceofspades]

With addon domains you could do addon.com/forums

addon.website.com/forums or website.com/addon/forums. It is the same exact thing to the server.