Wow, that's some funky code there. Rearrange it a little and you get what you wanted:

@ID = (1,1,1,1,1,1,1,1,2,2,2,2,2,2,3,3,4,4,4,4,4,5,5,5,5);

$evr_id = undef;
$count = 0;
$flag = 0;
$processed = 1;

print "\n";

foreach $a (@ID)
{
    if ($evr_id != $a) {
       $count = 1;
       $evr_id = $a;
       print "\n$processed) $a-$count\n";
    } else {
        $count++;
        print "$processed) $a-$count\n";
    }
    $processed++;
}
[download]

If you just want counts, then you probably want the other two solutions. If you're looking for series, then this would probably be preferred.