You have one anonymous array [-1, .... -1] for all objects.

If you will create an array inside new the error disappears

sub new {
    my $that  = shift;
    my $class = ref($that) || $that;
    my $self  = { 
    __name   => undef,
    __mpp    => [ (-1) x 10 ]
    };
    bless $self, $class;
    return $self;
}
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