problem with custom BBCode

I tried to create inline code BBCode, but it doesn't work the same way as default code BBCode does. When I put inside created inline BBCode part of another BBCode it breaks the post. I asked for help on phpBB.com forum and was told to report it to tracker as it can be problem with BBCode parser.

Here is discussion on phpBB.com with example (it also can serve as demo, because it works the same way as on my site.)