Some bbcode is not going to work for a little bit. It is in response to an outstanding security hole in phpBB. Normally I let things like this slide, but it has been out for several days. If I had more time I would patch it myself.
So, if you want to use the [url] BBCode, then you have to call it like so :
It should only be like this until at latest Thursday, when I finish my finals and I'll be able to spend some more time on code.