Changing the SF constructor to:

sub new {
    my ($class, $str, @lists) = @_;
    my @list = map {'ARRAY' eq ref $_ ? @$_ : $_} @lists;
    return bless {str => $str, list => \@list}, $class;
}
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fixes the list concatenation issue. The ordering issue is fixed by changing the first few lines of catSF to:

sub catSF {
    my ($lhs, $rhs, $inv) = @_;

    ($lhs, $rhs) = ($rhs, $lhs) if $inv;
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