base.tgz can't create 'usr/bin/mail' - cross compiled release 6.1

[qabulin <qabulin%gmail.com@localhost>]

Hello.

I’ve attempted a number of cross compilations of stable release 6.1, but I cannot manage to get usr/bin/mail to extract not matter what I try or repeat attempts.
$ su root ./build.sh -O ../obj/ -T ../tools/ -D ../dest/ -R ../release/ -U -m amd64 -V INSTALLSETS="base etc" install=/Users/qabulin/Downloads/netbsd-build/test/
[—snippet—]
Copying set base
pax: Cannot link file /Users/qabulin/Downloads/netbsd-build/test/./usr/bin/Mail to itself
[—snippet—]
ERROR: Failed to make installworld to /Users/qabulin/Downloads/netbsd-build/test/
*** BUILD ABORTED ***

I confirmed that the base.tgz found in the release dir does not extract usr/bin/mail :
$ cp ../release/amd64/binary/sets/base.tgz .
$ tar -xzpf base.tgz
./usr/bin/mail: Can't create 'usr/bin/mail'
tar: Error exit delayed from previous errors.
$

This is what does get extracted:
$ ls -la usr/bin/mail*
lrwxr-xr-x  1 qabulin  staff      21 Mar  1 21:55 usr/bin/mailq -> /usr/sbin/mailwrapper
-r-xr-xr-x  1 qabulin  staff  203400 Mar  1 21:55 usr/bin/mailx

What can I do to troubleshoot this further?  FYI, my cross compile build machine is a Mac:
$ sw_vers
ProductName:    Mac OS X
ProductVersion: 10.10.2
BuildVersion:   14C109

I really want to cross compile this locally without having to spin up a virtual box or digging up hardware for a build machine, so any hints or suggestions to try and resolve this would be appreciated.  I’m also new and would like to understand better what I’m dealing with here.

Regards,
qab