pfSense

On 2.2 I tried adding a few limiters and children and then deleting ones in the middle of the list... It seems that current code rewrites the limiter numbers after each delete/disable so that there is no gap. Actually those numbers do not seem to be in the config like that anyway, they are generated on the fly. I was executing this bit of code to see what was happening to the numbers:
include_once("shaper.inc");
read_dummynet_config();
$nextnum = dnqueue_find_nextnumber();
var_dump($nextnum);

$dnused = array();
    if (is_array($dummynet_pipe_list)) {
        foreach ($dummynet_pipe_list as $dn) {
            $tmplist =& $dn->get_queue_list();
            foreach ($tmplist as $qname => $link) {
    var_dump($qname);
    var_dump($link);
                if ($link[0] == "?")
                    $dnused[$qname] = substr($link, 1);
            }
        }
    }
    var_dump($dnused);

And ended up with this result:
int(3)
string(9) "MyLimiter"
string(1) "1"
string(4) "MyL2"
string(1) "2"
string(5) "Lim21"
string(2) "?1"
string(4) "Lim3"
string(1) "3"
string(5) "Lim31"
string(2) "?2"
array(2) {
["Lim21"]=>
string(1) "1"
["Lim31"]=>
string(1) "2"
}

And during the testing I had the last array with more entries in it, always with numbers "1" "2" "3" ... in order.
So I suspect that is why not everyone is seeing this bug. It only happens if you somehow have a limiter config that gets gaps in it.
In any case, if there is a gap, the code does not fill it in correctly, as you point out. The fix you suggest looks the right thing to do.
You could go to https://github.com/pfsense/pfsense and make the change and submit a pull request - it is very easy to do online for small changes like this.

Applied in changeset 8105ffa61c2d5aba42fa0ceac92ae7f9f80f8b19.