Directory truncation from 4.3bsd?

[David Robinson]

4.3BSD added the wonderful feature that a directory with unused disk
blocks at the end is truncated when a file is created, since create has to
search the entire directory anyways it can also detect empty directory
entries.

On our Suns running 4.0.1 this does not seem to be happening, I have
noticed emtpy directories that are over 100K in size, most notable
/usr/spool/news/.rnews and /usr/spool/mqueue.  I know that the 3.X NFSSRC
is based on 4.2BSD ufs code and does not have it but I thought that 4.0
would pick up the 4.3bsd features.  

Anyone have any insight on if this was deliberate or just an oversight?

	David Robinson		elroy!david at csvax.caltech.edu     ARPA
				david at elroy.jpl.nasa.gov	  ARPA
				{cit-vax,ames}!elroy!david	  UUCP