Hey,
I am not sure if this is fixed already, but I just found a bug under UILabel's GetUrlByCharacterIndex method.
It lacked another check for ending the url bbcode, the [/url] part. So if you click on any words that come after an already enclosed url, it will always return the url instead of null.
This is my solution to the problem:
int urlEnd = mText.IndexOf("[/url]", linkStart);
if (characterIndex > linkStart &&
characterIndex < urlEnd)
I just ran a little test and it solved pretty well, but I'm not sure if this is the best solution.