php header redirect before database insert - php

Question

My php header("Location: example.com") seems to redirect before the database query is inserted (on one computer). Which imo is weird, because I check if the database returns true before header runs.
This works fine for me, but on my friends system it seems to redirect too early. If I remove the header() function and die(). It inserts fine.
This is coded as an Extension to mediawiki. I dont know if the problem lies here. Mediawiki has its own database query class and functions.
if ($_GET['action'] == 'postReply') {
$threadid = $_POST['t_id'];
$content = $_POST['content'];
$postReply = postThreadReply($threadid, $username, $userid,
$content);
if ($postReply == 1) {
header("Location: ?title=" . $title . "&t=" . $threadid . '#last');
die();
}
This code is adapted to be read easier.
This is the main function which the header redirects too early.
postThreadReply() do some checks and inserts into the correct tables. postThreadReply() returns 1 if each query returns true.
I don't think more code is necessary, but let me know if it is. :)
So I'm wondering if there is something wrong with my code, or within Mediawiki? Or is this a known issue with the header() function? Is there any alternative method I can try?
This is my first question here, so I'm sorry if my question is unclear or I dont provide enough code.
EDIT:
postThreadReply()
function postThreadReply($threadid, $username, $userid, $t_post) {
if (postExistDuplicate($threadid, $username, $userid, $t_post)) return 3;
if (!threadExist($threadid)) return 4;
$inpost = insertPost($threadid, $username, $userid, $t_post);
if (!$inpost) return 2;
return 1;
}
insertPost()
function insertPost($threadid, $username, $userid, $t_post) {
$datetime = date_create()->format('Y-m-d H:i:s');
$dbw = wfGetDB( DB_MASTER );
$res = $dbw->insert(
'disc_posts',
array(
'id' => null,
'thread_id' => $threadid,
'author' => $username,
'author_id' => $userid,
'content' => $t_post,
'posted' => $datetime,
'deleted' => 0
)
);
return $res;
}
^ Mediawikis way of doing queries.