BBCode parser doesn't properly check for closing ']'

It appears the BBCode parsing engine only pattern matches to the start of a BBCode and doesn't check for the closing square bracket, resulting in false matches and incorrect output.

For example, posting the follow

So, [I tell people to drill down into that index]. What are you buying? Look behind the curtain. Your largest investment is Britain. Your second-largest investment is Japan. Your third-largest investment is France.

In the resultant output, the quoted text inside the square brackets,
[I tell people to drill down into that index]
goes missing and all remain text is italicized.