Where is the logic located which determines the tpl file for the front page? We are using Drupal 6. When accessing http://www.mysite.com/, the tpl file which is displayed is named page-front_page.tpl.php. I cannot figure out where the logic is which decides that page-front_page.tpl.php will be used for the front page. 

I created a second file, named page-front.tpl.php, and this will display instead of page-front_page.tpl.php, seemingly bypassing page-front_page.tpl.php.

Does anybody know how page-front_page.tpl.php is defined as a front page? Or is there some sort of automatic URL parsing happening here?

Edit 1.0: Please read my comments to answers below for more information.
please review in /includes/theme.inc near to the line if (drupal_is_front_page()) {...

if (drupal_is_front_page()) {
    $suggestions[] = 'custom-page-front-name-here';
  }


I changed the $suggestions[] value, and I saw that .tpl.php name to the front page can be customized.

According the comment of nmc, 


  this file/code should not be modified as it is part of Drupal core


. this is only to locate where can be stablished the value.