Nmap 3.81: warning accompanies netmask /1

[Justin Cranford <jcranford () n-able com>]

I get a warning with all versions of nmap (including 3.81) when I run
this command:

   nmap 10.0.0.0/1

The error is:

   Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2005-02-08
10:24 EST
   WARNING: No targets were specified, so 0 hosts scanned.
   Nmap finished: 0 IP addresses (0 hosts up) scanned in 0.006 seconds

This only happens when I specify netmask /1. I tried all other netmasks
from 0-32 and they scan ok. For example:

nmap 10.0.0.0/0
nmap 10.0.0.0/2
nmap 10.0.0.0/24
nmap 10.0.0.0/32

Is this a bug?