OK, you can replace it with the original script now.
I think I've finally figured this out, and it appears to be the most ridiculous thing ever.
This is part of the javascript in thread.js for when it gets the result of the AJAX request:
else if(request.responseText.match(/id="post_([0-9]+)"/))
{
var pid = request.responseText.match(/id="post_([0-9]+)"/)[1];
var post = document.createElement("div");
post.innerHTML = request.responseText;
$('posts').appendChild(post);
if(MyBB.browser == "ie" || MyBB.browser == "opera" || MyBB.browser == "safari" || MyBB.browser == "chrome")
{
var scripts = request.responseText.extractScripts();
scripts.each(function(script)
{
eval(script);
});
}
Form.reset('quick_reply_form');
if($('lastpid'))
{
$('lastpid').value = pid;
}
}
else
{
request.responseText.evalScripts();
}
If it gets a post back, it'll do all the stuff to show the post, if it doesn't get a post, it runs the last bit at the end. When I added the debug stuff, I could see that it was going into that last bit, and getting no further (in the code after what's here), which was weird; it seemed to be getting stuck there, but I couldn't work out why it was going here at all. Then I had a closer look at your source code. Look at this javascript:
request.responseText.match(/id="post_([0-9]+)"/)
it's matching:
id="post_([0-9]+)"
i.e. post_ and then a number; the number of the post. However, on your forum, it has this:
id=post_188679
This has no ", so quite simply, it didn't match the pattern for the javascript above to register it as a post, because the " were missing.
I'm not sure why it's like this in your forum or if it's intentional, but either way, in the postbit and postbit_classic template, on one of the first few lines, it
should have this right at the end of the long opening <table> tag:
id="post_{$post['pid']}"
however yours will probably just be this:
id=post_{$post['pid']}
Add the " " around it again, and it should work.