Greasemonkey script breaks the Forum?

[hanst99]

I hope this is the right section to post this- I have written a Userscript with the following content:

var tag = document.createElement('script');
tag.type='text/javascript';
tag.src='http://latex.codecogs.com/editor3.js';
var head = document.getElementsByTagName('head').item(0);
head.appendChild(tag);
var body = document.body.innerHTML;
document.body.innerHTML = '<input type ="button" value="CodeCogs LaTeX editor"\
 onclick="OpenLatexEditor(\'\',\'html\',\'\')"/>'+body;

If I use it on this site, I can no longer use the reply button. (nothing happens anymore if I press it) Now I gotta admit my knowledge about javascript is rather, eh, limited to say it euphemistically. So what I am asking is:
1) What in my script would cause this behaviour?
2) How do I fix this (if it is fixable. For now I am just excluding cplusplus.com, but that's not really a permament solution now, is it?)