trying to figure out win32 STDIN hang with IPC::Open2

main.pl

$arg = ' ' . shift @ARGV;
$script = qq[perl pipe1.pl $arg];

system(q{perl -e "print qq[hi$/there$/]" | } . $script);

use IPC::Open2 "open2";
$pid = open2($out, $in, $script);

$|=1;
print $in qq[hi$/there$/];
close $in;
print scalar <$out>;

unless( $arg =~ /2/ ){
  close $out;
  waitpid $pid, 0;
}

pipe1.pl

warn "STARTING\n";

# this prints first line but not second... without neither print
$|=1 if @ARGV;

$fh = \*STDIN; while(defined($_ = <$fh>)){ print qq[  $_] }

main.pl hangs
main.pl 1 prints the first line, then hangs
main.pl 2 prints the first line (not the 2nd) and exits