Because each iterates over each key and value and keys and values reset that iterator back to the beginning.

You want to get the value of keys before you iterate through the hash with each:

my %hash = qw( a 1 b 2 );
my $count = 0;
my $key_count = keys %hash;
while ( my ( $key, $value ) = each %hash )
{
   $count++ if $value == $key_count;
}

print $count;
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