Why is single reducer called twice?

[Mark Kerzner]

Hi,
In my code, I set the number of reducers to 1,

conf.setNumReduceTasks(1);

and it all works as intended, but I notice that the reducer is called a
second time to do nothing, before all is done. Can I use this side effect to
close the static resources (like a zip output stream) that I open on the
first call?

Thank you,
Mark