Hi Niko. I tested again. I installed Extra Userfield-V1.2 to Q2A-V1.5. I can't reproduce the phenomenon of Niko. "SS6" is qa-page-user.php. There is two change. Check changes part once again. Moreover, when checking SQL, use debug option of QAROOT/qa-config.php.
define('QA_OPTIMIZE_LOCAL_DB', true); // false -> true
define('QA_DEBUG_PERFORMANCE', true); // false -> true
Right SELECT query is ...
SELECT fieldid, title, content, flags, position, extra FROM qa_userfields
Finally, If screenshot exists, post to answer instead of comment.
Thanks.