We were having trouble with bogus routes being added when using a
netmask of 255.0.0.0, which we tracked down to a problem in
/usr/src/sys/netinet/in.c.  Here's the version information, followed
by the diff:

/*	$NetBSD: in.c,v 1.14 1994/06/29 06:38:00 cgd Exp $	*/
...
 *	@(#)in.c	8.2 (Berkeley) 11/15/93


*** in.c.orig	Thu Nov  3 09:42:57 1994
--- in.c	Thu Nov  3 09:43:45 1994
***************
*** 147,153 ****
  	register char *cp = (char *) (&ap->sin_addr + 1);
  
  	ap->sin_len = 0;
! 	while (--cp > cplim)
  		if (*cp) {
  			(ap)->sin_len = cp - (char *) (ap) + 1;
  			break;
--- 147,153 ----
  	register char *cp = (char *) (&ap->sin_addr + 1);
  
  	ap->sin_len = 0;
! 	while (--cp >= cplim)
  		if (*cp) {
  			(ap)->sin_len = cp - (char *) (ap) + 1;
  			break;