BBCode not working once plugin is Activated

[ThistleProse]

For some reason most (but not all?) BBCode is not working once the plugin is activated. I disabled the plugin to confirm.

You can view an example here: https://blood-ties.net/rp/showthread.php?tid=125
You will need to scroll a little bit, but you can see how the BBC works for some posts, and then stops.

I'm not sure why this is happening or how to fix it, so any assistance would be greatly appreciated :)

[ThistleProse]

I temp fixed the URL borken issue by re-creating the [URL][/url] code as follows, rather than using the default given by myBB