$i is an element from @$aref. You're treating it like an index. Try:

Two ways:

c:\@Work\Perl\monks>perl -wMstrict -MData::Dumper -le
"my $aref = [
   [ 'kept',    82 ],
   [ 'notkept',  1 ],
   [ 'repaired', 3 ],
   ];
 print Dumper $aref;
 ;;
 for my $i (0 .. $#$aref) {
   printf qq{label $aref->[$i][0]  };
   }
 print qq{\n ---------};
 ;;
 for my $aref_2nd_level (@$aref) {
   printf qq{label $aref_2nd_level->[0]  };
   }
"
$VAR1 = [
          [
            'kept',
            82
          ],
          [
            'notkept',
            1
          ],
          [
            'repaired',
            3
          ]
        ];

label kept  label notkept  label repaired
 ---------
label kept  label notkept  label repaired
[download]

my $table = [
   [
      'kept', 82
   ],
   [
      'notkept', 1
   ],
   [
      'repaired', 3
   ]
];

for my $i ( 0 .. $#{ $table } )     # Iterates over the indexes.
{
   say "label ". $table->[$i][0];
}
[download]

for my $row ( @{ $table } )         # Iterates over the values.
{
   say "label ". $row->[0];
}
[download]

Foreach loop provides list context, so foreach my $i ( @{ $aref } ) explodes into its elements

foreach my $i( ['kept', 82], ['notkept', 1], ['repaired', 3] ) { ...
# so $aref->[$i][0]
# looks like $areg->[ ['kept', 82] ][0]
#
[download]

$ perl buggy_array.pl 2> out.txt

(it hangs here, press Ctrl-C to stop)

$ head -6 out.txt
Use of reference "ARRAY(0x1cfb148)" as array index at ary.pl line 21.
Use of uninitialized value in concatenation (.) or string at ary.pl li
+ne 21.
Use of reference "ARRAY(0x1d0fad8)" as array index at ary.pl line 21.
Use of uninitialized value in concatenation (.) or string at ary.pl li
+ne 21.
Use of reference "ARRAY(0x1d0fbf8)" as array index at ary.pl line 21.
Use of uninitialized value in concatenation (.) or string at ary.pl li
+ne 21.
[download]

perl -E 'my $aref=[undef]; say 0 + $aref'
19468616
[download]

$areg->[ ['kept', 82] ][0]

# becomes something like
# $areg->[ 9999999 ][0]
# (or whatever the memory address of that array is...)
[download]

perl -E 'my $aref=[undef]; $aref->[1000][0]; say scalar @{ $aref }'
1001
[download]

So, now your $aref has tons of of undefs. So the loop keeps looping and issuing warnings.

So yeah, all in all, that was a pretty interesting question, I must say.