I have a file:

<?php
print ini_get('upload_tmp_dir') . '<br>';
?>

And I have multiple virtual host specifications like:

{Domain names and file paths have been changed to protech the innocent...}

<VirtualHost site1.com>
ServerName myapp.site1.com
ServerAdmin webmaster@site1.com
DocumentRoot /home/mainapplication
php_admin_value upload_tmp_dir /home/client1/tmp
php_admin_value error_log /home/client1/log
php_value error_reporting 7
php_flag display_errors On
php_flag log_errors On
php_flag register_globals on
php_flag display_errors off
</VirtualHost>

<VirtualHost site2.com>
ServerName myapp.site2.com
ServerAdmin webmaster@site2.com
DocumentRoot /home/mainapplication
php_admin_value upload_tmp_dir /home/client2/tmp
php_admin_value error_log /home/client2/log
php_value error_reporting 7
php_flag display_errors On
php_flag log_errors On
php_flag register_globals on
php_flag display_errors off
</VirtualHost>

N.B. When using PHPA, the problem is incredibly obvious (changes continuously), however with it removed, and reloading the page HUNDREDS of times, I saw this happen twice.

The only values displayed are those of ACTIVE virtual servers... at least that is what seems to be happening.