my @due=sort chomp (my @lines=<STDIN>);
[download]

is basically

my @anon = chomp (my @lines=<STDIN>);
my @due=sort @anon;
[download]

It is not the same as

chomp (my @lines=<STDIN>);
my @due=sort @lines;
[download]

In the first snippet you posted, you are sorting @lines. In the second, you are sorting the result of chomp. These are very different, as described in chomp's documentation.