Modifying Register.php

[Hisoka96]

Hi guys i was trying to modify some custom fields in my register.php and foundt up an interesting thing.

For the debug i've used a .txt file to see if return the right things in the field,used the following code:

$myfile = fopen("newfile.txt", "w") or die("Unable to open file!");
$txt = $vbulletin->GPC['username'];
fwrite($myfile, $txt);
fclose($myfile);

And that works for every field but not for Password or Confirmpassword.
I actually know that password works just fine and don't need debug but i'd like to know why that exception happen,in the .txt file i can find every field but not password.

Why?