Working on a new release of Preg question type we found out that PHP 5.6 and higher have a nasty bug with long arrays, which make Preg question type completely unworkable. It is described in https://bugs.php.net/bug.php?id=68057 . However, there is no work on the bug for the half year for now.
Anyone who interested in Preg question type or generaly want to help please vote for it by the link above and comment there. The bug includes PHP file needed to reproduce it.