I've narrowed it down to passwd

my $exp = Expect->new("passwd fred") or die "Cannot spawn: $!\n";

$Expect::Exp_Internal = 1;

my $timeout = 5;

$exp->expect($timeout,
         [ 
          qr/UNIX password:/ => sub {
        my $exp = shift;
        $exp->send("sponge\n");
        exp_continue; 
          } 
         ],
        );

$exp->soft_close();
[download]

Get either timeout, but add a ; to the end of the command and it works fine.