I am sure this is NOT a bug in the documentation. There is no such thing as "interesting" match unless it can be described mathematically. Instead, the documentation 
specifies _precisely_ what exactly the function must do in a very precise manner.

The problem is that it does a different thing.

Another issue of this algorithm is that it uses a quite slow algorithm. It's computational complexity is O(n*m). Another one based on generalized suffix trees has a much more modest complexity O(n+m). The details are here:
http://en.wikipedia.org/wiki/Longest-common_substring_problem