CakePhp 3.x, TCPDF, htmlspecialchars

After trying to find and debug the same error for over an hour, I just reset the value to UTF-8 after the usage of TCPDF - and everything works like before:

$pdf = new TCPDF('P', 'mm', 'A4', true, 'UTF-8', false);

///...create, save, display your pdf

// Reset the encoding forced from tcpdf
mb_internal_encoding('UTF-8');

I also tried resetting it directly after the call of new TCPDF and everything was fine, too. I don't know what could go wrong with this reset :) My PDFs still look the same after this but emails get send again.