This is what I got from your script above:

P:\test>426324
GOT PAGE: 61833 bytes
GOT PAGE: 61456 bytes
INC:
AutoLoader.pm
Carp.pm
Config.pm
DynaLoader.pm
Exporter.pm
Exporter/Heavy.pm
Fcntl.pm
Storable.pm
Thread/Isolate.pm
XSLoader.pm
attributes.pm
c:/Perl/lib/auto/Storable/_freeze.al
c:/Perl/lib/auto/Storable/autosplit.ix
c:/Perl/lib/auto/Storable/freeze.al
overload.pm
strict.pm
threads.pm
threads/shared.pm
vars.pm
warnings.pm
warnings/register.pm
        (in cleanup) Can't call method "PUSH" on an undefined value at
+ c:/Perl/site/lib/Thread/Isolate.pm line 224 during global destructio
+n.
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And this is what I got from my equivalent:

P:\test>426297
GOT PAGE: 61637 bytes
GOT PAGE: 61585 bytes
AutoLoader.pm
Carp.pm
Config.pm
DynaLoader.pm
Exporter.pm
overload.pm
strict.pm
threads.pm
vars.pm
warnings.pm
warnings/register.pm
[download]

Rather less loaded?

The script I used was:

#! perl -slw
use strict;
use threads qw[ async ];

my $thr = async {
    require LWP::Simple;
    return LWP::Simple::get( 'http://www.perlmonks.com/' );
};
print 'GOT PAGE: ', length $thr->join, ' bytes';

$thr = async {
    require LWP::Simple;
    return LWP::Simple::get( 'http://www.perlmonks.com/' );
};
print 'GOT PAGE: ', length $thr->join, ' bytes';

print for sort keys %INC;
[download]