How can I to keep an accurate count of rows by category?

Here is my situation: I have a table with about 500+ items, each of them labelled with a status: running, pending, or dead (these are linux systems being monitored).

Basically, the page should be like this:

total count: count_total, running: count_running, pending: count_pending, dead: count_dead
table here

Here is an appropriate excerpt of the datatables setup:

function clr_count() {
  count_total = 0; $('#disp_total').text(count_total);
  count_dead = 0; $('#disp_dead').text(count_dead);
  count_pending = 0; $('#disp_pending').text(count_pending);
  count_running = 0; $('#disp_running').text(count_running);
}

function set_count(status) {
  count_total++; $('#disp_total').text(count_total);
switch(status) {
case 'running': count_running++; $('#disp_running').text(count_running); break;
case 'pending': count_pending++; $('#disp_pending').text(count_pending); break;
case 'dead': count_dead++; $('#disp_dead').text(count_dead); break;
}}

  $(document).ready(function() {
  var oTable = $('#monitor').dataTable( {
  "bJQueryUI": true,
  "bProcessing": true,
  "bPaginate": true,
  "bStateSave": true,
  "bInfo": true,
  "sScrollX": '100%',
  "aLengthMenu": [[10,25,50,100,-1],[10,25,50,100,'All']],
  "sAjaxDataProp": "data.aaData",
  "sAjaxSource": '/api/Impact/list?group=canada-post;fmt=json',
  "aoColumnDefs": [
  { aTargets: [ 0 ], sClass:"tabBodyColAlert", sWidth: "16px" },
  { aTargets: [ 1 ], sClass:"tabBodyColStatus", mRender:function ( data, type, full ) { set_count(full[1]); return set_status(full[1]); }},
.....
  "fnPreDrawCallback": function ( oSettings) {
      clr_count();
  },
....

Here is what happens:
1. When the table is drawn from scratch, the mRender function for cell 1 is called three times, sometimes four. This happens twice between the first fnPreDrawCallback call and the second, and once after the second. If I don't clear the count (via the fnPreDrawCallback function) it reflects three times the count. However, with the clear, the final count is all right. (fnPreDrawCallback is effectively called twice, as others have mentioned)

2. If I filter the table, fnPreDrawCallback clears the counts, the mRender function is called for each result, and the new count is correct, reflecting the result of the filter.

3. But if I change the number of lines per page, for example from 10 lines to 25 using the drop down, without reloading the page, the fnPreDrawCallback clears the count, and the row rendering functions are not called, so the count stays at 0. I've tried using fnDrawCallback, fnHeaderCallback, fnInfoCallback, and they all seem to work in lockstep; I have been unable to find a way to get the count to stay when changing pagination. I attempted to check several properties in the oSettings object, but was unable to identify one that didn't break something else.

Is there any way to do what I want to do? I'm nearly there, if I could tell fnPreDrawCallback not to clear on a pagination change, it would be perfect.
Of course, I'm curious as to why the mRender function is called several times, as I have several cases where I expect to use the mRender function.