Integrating BBcode parsing in a hackish mod

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Hi. I've been writing a VERY crude addon to my forum which is basically a PHP/AJAX chat system. It's not deeply integrated with vB, and is using its own tables while being a templated PHP file. However, I've been trying to make it so that users can enter BBcode and have it parsed in the chat, ex:

PHP Code:

Jimmy bob, did you even [b]HEAR WHAT I SAID[/b]?? [i]Well?[/i] 


Should appear with the proper HTML instead of BBcode.

I've been using this tutorial for the BBCode parsing.

However, a *LOT* of funky stuff happens. Here's how the chat itself works, in a nutshell.

AJAX refreshes chat every XX seconds, PHP file returns latest XX messages pulled from DB, executing bbcode_parse on each of them before returning.
If user sends message, PHP file inserts message into DB.

The chat itself works fine, the problem is that the bbcode_parse will horribly mutilate the message. Example:

PHP Code:

<<<<<<<<<<<<<>>>>>>>>>>>>>>> <b>test!</b> [b]test![/b] 


turns into

PHP Code:

<<<<<<<<<<<<<>?&#402;????>>ˆ??\?O؏ˆ?—]\?V??— 


If the message had htmlentities() run on it before insertion into DB, the text is *slightly* less mutilated.

Is there some bbcode_parsed_decode or something I'm missing here? Any help would be greatly appreciated!