I share this.. Perhaps something to add to next version of mantis.. I am using hidden styles to hide PLATFORM, OS, AND OS VERSION with a link that will show the feilds if no profile exists. I just didnt like the fact that when you select a profile, the feilds are not populated automatically. I found that confusing. So rather than reprogramming the logic, there is a very simple solution.

1. In strings_language file (i.e. strings_english.txt), put in the following text:
   $s_or_fill_in = 'IF A PROFILE IS MISSING FROM DROPDOWN BOX ABOVE, FILL IT IN
   MANUALLY';

2. Then in bug_report_advanced_page.php look for the <?php echo lang_get( 'or_fill_in' ) ?> tag.. Just before it, put in the following:

<style type="text/css">
#platform {visibility:hidden;}
#os {visibility:hidden;}
#os_build {visibility:hidden;}
</style>

Then just after it, put in the following:

 <a href="#" onClick="document.getElementById('platform').style.visibility='visible'; document.getElementById('os').style.visibility='visible'; document.getElementById('os_build').style.visibility='visible'; ">BY CLICKING HERE.</a>

YOU ARE NOW DONE.

This will basically hide the 3 feilds when the page is loaded. If the enduser does not see a profile in the dropdown, he/she can click the link to show the 3 feilds and enter the info manually.

Note: If you like, you can make a link that hides the boxes again. Just use something like this:

 <a href="#" onClick="document.getElementById('platform').style.visibility='hidden'; document.getElementById('os').style.visibility='hidden'; document.getElementById('os_build').style.visibility='hidden'; ">HIDE ME.</a>

If you want, you can use the config.inc file to define this style sheet quasi-code and then turn this "function" on and off.