I made a survey having questions with codes k1, k2 and k3. If I run export_responses() having for example array("seed", "datestamp") as the last argument and "csv" as sDocumentType, I get CSV file with those columns. If I put null as the last argument, I got CSV of all data, including columns k1, k2 and k3. But if I use for example array("id", "k1") as the last argument, then column for k1 is always empty.

I am using PHP and have

require_once '/var/www/html/limesurvey/application/libraries/jsonRPCClient.php';

at the beginning of .php file.