As per a topic in the support forum, http://forum.nzbget.net/viewtopic.php?f=3&t=1776, it was confirmed that "Extra directory per nzb is a correct behavior".
I would like to request a feature whereby for a given category this extra directory is not completed.
For example, downloading an NZB called "NZB Title" containing a single MP4 called "Show Title" extracts to:
c:\DestDir\NZB Title\Show Title.mp4
I would like the option, on a category basis, for it to extract to:
c:\DestDir\Show Title.mp4