theme_table override / hook not working

I am trying to override / hook theme_table from theme.inc.
My theme name is stat.
I have added following function to my theme template.php.

function stat_table($variables) {
  //table logic here
  return $output;
}

I have dev env configured with xdebug and while function is 'loaded'/processed when displaying page with table, it is never called.
Original theme_table is called instead. I already tried clearing cache via drupal_theme_rebuild();

Is there anything I am doing wrong?
How can I debug why is the function not called?