When you are instantiating a nusoap try it like this:
$nuso = new nusoap_client('http://test.com/');
$nuso->soap_defencoding = 'UTF-8';
$nuso->decode_utf8 = false;
$res = $nuso->call('testFunction');
The issue seems to be when declaring the decode_utf8
parameter as true.
Hope it works.