Problem with the <!--more> tag

[Fonz]

When I apply that <!--more> tag in a post (via the WYSIWYG editor) it does split up the post and shows the "click here to read more" text on the index page of my blog.

Problem is my navigation menu on the, in my case, right drops all the way to the bottom of the blog and all post made before the post I split up "merge" in the post that I split up (this is still on the blog index).

Here's how the merge thing looks like:
http://www.thisisliveblog.com/pics/tilblog_screen.jpg

Don't mind the dutch

Does anyone has an idea how to solve this?