use Text::xSV;

my $parser = Text::xSV->new( filename=>$datafile, sep=>"\t" );
$parser->read_header;

my %data;
while (my $row_ref = $parser->get_row) {
    $data{ $row_ref->[1] } = $parser->extract_hash;
}
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The significant changes from your version are:

1. xSV doesn't default to a tab. You have to tell it that you want that.
2. You don't need to call open_file - it will do that for you if you pass the filename into the constructor.
3. The return of read_header cannot be relied on, so don't rely on it.
4. I'm using the return of get_row directly. Yes, you can mix positional and name-based logic in Text::xSV.
5. Your slicing logic was buggy. But luckily there is no need to do something that complex.

UPDATE: A closer reading of the original question shows that the format differs from the obvious. The first row has an extra # in it that is not lined up with the other fields and needs to be discarded. Here is a solution to that variant:

use Text::xSV;

my $parser = Text::xSV->new( filename=>$datafile, sep=>"\t" );
my @headers = $parser->get_row;
shift @headers; # Get rid of the unwanted #
$parser->bind_fields(@headers);

my %data;
while (my $row_ref = $parser->get_row) {
    $data{ $row_ref->[1] } = $parser->extract_hash;
}
[download]