When making a custom BBCode and trying to nest, it will end on the wrong BBCode ending. For example:

If you use the top example on the Add BBCode page (for highlight) and try to use the highlight like this:

[highlight=red]the pen is [highlight=blue]BLUE![/highlight] not red[/highlight]

It will return:

the pen is [highlight=blue]BLUE!

highlighted in red and

not red[/highlight]

unformatted.

Image: Top is the BBCode screen, bottom is the output. Click for full size
!http://img296.imageshack.us/img296/3636/bberrorzu0.png