TCPDF UTF8 - weird spacing between characters

Question

Pls have a look at the following picture http://dev.mosaicware.pl/tmp/PDF-utf-problem.png

As you can se PL and RO characters are looking weird, they look fine on the webpage. Any clue? I've used arialunicid0 font and following code (characters in DB are UTF-8):

$pdf = new models_PdfUtf(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', true); 
$pdf->SetFont('arialunicid0'); $pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, PDF_HEADER_TITLE, PDF_HEADER_STRING); 
$pdf->SetAuthor($problem . ' ' . $problem['user_surname']); $pdf->SetTitle($problem['problem_title']); 
$pdf->SetSubject($problem['problem_title']); 
$pdf->Output('export.pdf','I');
$pdf = new models_PdfUtf(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', true);
    $pdf->SetFont('arialunicid0');
    $pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, PDF_HEADER_TITLE, PDF_HEADER_STRING);
    $pdf->setPrintFooter(false);
    $pdf->SetAutoPageBreak(TRUE, PDF_MARGIN_BOTTOM);
    $pdf->AddPage();
    $pdf->writeHTML($c, true, 0, true, 0);
    $pdf->SetAuthor($problem . ' ' . $problem['user_surname']); 
    $pdf->SetTitle($problem['problem_title']); 
    $pdf->SetSubject($problem['problem_title']); 
    $pdf->Output('export.pdf','I');