When I transform your code into something I can run (it really does help us and you):

my @ICE = map { [ split /\s*\(tab\)\s*/ ] } <DATA>;
my %seen;

my @ICEU = grep { !$seen{$_->[0]}++ } @ICE;

print Dumper \@ICE;
print Dumper \%seen;
__DATA__
30F-WKS(tab)`1781183799.xxxx1' (tab)     IC---;
30F-WKS  (tab)   `1781183799.xxx11'  (tab)    IC---;
ADM34A3F9  (tab) `1781183799.41455'  (tab)    IC---;
[download]

I get

$VAR1 = [
          [
            '30F-WKS',
            '`1781183799.xxxx1\'',
            'IC---;
'
          ],
          [
            '30F-WKS',
            '`1781183799.xxx11\'',
            'IC---;
'
          ],
          [
            'ADM34A3F9',
            '`1781183799.41455\'',
            'IC---;
'
          ]
        ];
$VAR1 = {
          'ADM34A3F9' => 1,
          '30F-WKS' => 2
        };
[download]

Which looks pretty much as it should, doesn't it?

It looks like Hercynium is right. @ICE doesn't contain what you think it does