Problem using -X and -N together with gnutar?

[Robert Nicholson]

So I'm using

p1664-1222bkksp1:~ robert$ gnutar --version
tar (GNU tar) 1.14
Copyright (C) 2004 Free Software Foundation, Inc.
This program comes with NO WARRANTY, to the extent permitted by law.
You may redistribute it under the terms of the GNU General Public  
License;
see the file named COPYING for details.
Written by John Gilmore and Jay Fenlason.
Modified to support extended attributes.
p1664-1222bkksp1:~ robert$

and what I notice is that if I do a full backup with gnutar the  
exclusions in my exclusions file are correctly obeyed. However, if I  
want to do an incremental backup and use those same exclusions. What  
typically happens is that if the file has no entries then the backup  
is truely incremental. ie. it obeys the date of the file using via -N  
but if I have an entry in there the meaning of -N is lost altogether  
and it does a full backup ie. doesn't consider the modified time of  
the files.

Is this a know feature/bug?