Strange Behavior

I have a ..../public/test.php file:
<?php print_r(getallheaders()); ?>

and I have a CI app where in a before() function of a custom filter I have:
 log_message('debug', print_r(getallheaders(), true));

I'm getting different results for the 'Host' header. The first prints the domain name of my server and the second prints the IP address.
Does anyone know why this would happen?

Simpler is always better