PHP POST data in ASCII instead of UTF8 - php

Question

I have got problem with coding after sending data by POST from form.
When I am using special polish characters like ą, ć, ę, ł, ń etc. I am getting ? instead of proper character. I am struggling with it already third day and cannot find the problem.
Website is using UTF8 and all files are in UTF8. The form is sending data using AJAX and getting response using output buffer (ob). When I am checking headers in Chrome everything is alright. So it looks like something is happening with jQuery/Ajax/ob?
My all functions which are used for jQuery/Ajax/ob:
jQuery:
function ajaxForm(oform,ni,wt,nhi) {
if (wt==''||wt==undefined) {
if (oform.id=='theLongForm') {
// time out based on the form id
wt=120000;
} else if (document.forms[oform.id].timeout) {
// use the specific time out setting
wt=document.forms[oform.id].timeout.value;
} else {
// default time out setting
wt=10000;
}
}
if (ni==''||ni==undefined) ni=false;
if (nhi==''||nhi==undefined) nhi=false;
if (ni!=true) showIndicator();
$('#'+oform.id).ajaxSubmit({
url: oform.action,
type: 'POST',
dataType: 'xml',
timeout: wt,
error: function(){
document.forms[oform.id].ajax.value='x';
$('#'+oform.id).submit();
},
success: function(xml){
if (processResult(xml)) {
if (nhi!=true) $("#indicator").hide(200);
}
}
});
return false
}
PHP:
function outputAjaxHeader() {
global $ajaxRequest,$doneAjaxHeader;
if ($ajaxRequest && !$doneAjaxHeader) {
// output ajax XML header
header('Content-type: text/xml; charset: utf-8');
print '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
print '<items>' . "\n";
$doneAjaxHeader = true;
}
}
function outputAjaxItemStart($elem,$option='general',$full=false) {
global $ajaxRequest;
if ($ajaxRequest) {
print "\t" . '<item>' . "\n";
print "\t\t" . '<name>'.($full?'':'#').$elem.'</name>' . "\n";
print "\t\t" . '<option>'.$option.'</option>' . "\n";
print "\t\t" . '<data><![CDATA[';
ob_start();
}
}
function outputAjaxItemEnd() {
global $ajaxRequest;
if ($ajaxRequest) {
$buffer = ob_get_contents();
ob_end_clean();
print $buffer;
print ']]>' . '</data>' . "\n";
print "\t" . '</item>' . "\n";
}
}