inlinemod issue

[ForumJoiner]

I want to make a post for selling an eBook, using PayPal.
I insert both buttons ("Add to cart" and "View car"), having HTML editing allowed.
When I preview the page, everything works fine.
When I save it, the first button, "Add to cart", points to inlinemod.php, instead of
pointing to PayPal.

Looking up the source code of the page, I see on line 581,
<!-- / close content container -->
<form action="inlinemod.php?threadid=5&amp;p=5" method="post" id="inlinemodform">
That form is not closed anywhere. If I add an </form> and save that page as HTML,
everything works fine.
What can I do to fix the problem?

I'm running Internet Explorer 7, under Windows Vista Home Premium.
Mozilla Firefox 2 works just fine, without </form>.

[Spank]

If it works fine with the </form>
what's the problem?

[ForumJoiner]

If it works fine with the </form>
what's the problem?
The page that the user sees on my site does not have the </form> closing tag generated automatically by vBulletin.
I opened the HTML source of the generated page, I manually added the </form> closing tag to see if it solves the problem and saved the page to my local computer, to test it.

The above procedure was only for testing. I can't ask the visitors of my site to see the source code of the page, add the </form> closing tag and save the page locally in order to see it properly. I want to ask vBulletin to do it all the time, but I don't know how.

Does anyone, please?

--------------- Added at 21:53 ---------------

I noticed that the problem appears only when I'm logged as admin.
When I am logged as a regular user or not at all, everything is fine.

What is inlinemod.php doing anyway? Can be disabled?

[Spank]

On what page is the problem occuring?

inlinemod.php allows for closing/moving threads etc from the forum.