I learnt this from The Perl Black Book...

You need to review the lessons.

Your prototype means that any optional hashref supplied will be assigned to the array, and will never get assigned to the appropriate place inside the sub:

sub test($@;\%){ 
    my( $scalar, @array, $hashref ) = @_; 
    pp $_ for $scalar, \@array, $hashref;
};;

$s='fred'; 
@a = 1..10; 
%h = 1..10;;

test( $s, @a, \%h );;
"fred"

[
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  10,
  { 1 => 2, 3 => 4, 5 => 6, 7 => 8, 9 => 10 },
]

undef
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