That's strange. Using OP's code on 5.24.0, it breaks. If I swap those two lines around, it works fine. I've never had an issue with assigning values to an array out of order before, but in this case, it definitely matters :)

Works:

use warnings;
use strict;

my $value = "A\tB\tC\tD\tE\tF\t\t\t\t\t\t";
my @flds = split(/\t/, $value);
$flds[8] = 0;
$flds[16] = undef;
print scalar @flds;

__END__
17
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Borked:

use warnings;
use strict;

my $value = "A\tB\tC\tD\tE\tF\t\t\t\t\t\t";
my @flds = split(/\t/, $value);
$flds[16] = undef;
$flds[8] = 0;
print scalar @flds;

__END__
Modification of a read-only value attempted at split.pl line 7.
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That's strange.

Yup

While keeping in mind Re^3: split problem ( Modification of a read-only value attempted , Devel::Peek )

Try adding Data::Lock

use Data::Lock qw/ dunlock /;
dunlock(@flds);
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