Here's a simpler test case that uses only core modules.  It works fine 
under 5.8.8, but crashes under 5.10.0 (on Linux, anyway).  It should 
print "ok\n".

#! /usr/bin/perl
use strict;
use warnings;
use Tie::Hash ();

my %h;
tie(%h, 'Tie::StdHash');

$h{key} = 'ntp-2 ntp2 ntp-pa ntp-2-pa ntp2-pa ';
$h{key} =~ s/(^|\s)ntp2-pa\s/$1/;

die "not ok: <$h{key}> \n"
     unless $h{key} eq 'ntp-2 ntp2 ntp-pa ntp-2-pa ';

print "ok\n";

-- 
Chris Madsen                                          perl@[...].net
   --------------------  http://www.cjmweb.net  --------------------