Allow me to rephrase the full steps to reproduce.

• Go to a course.
• Open question bank import and do "Import questions from file" taking the attached file "questions-Physics-Default for zzz-20120206-1453.xml" in file formet "Moodle XML format".
• Stay in question bank but go to questions.
• Select category "Default for zzz".
• Edit the question "zzz Force of two 1 kg masses..." (clicking on the gear).
• At the bottom of the following page, click "Save changes".
• In the next page, leave "Synchronise the data from shared datasets with other questions in a quiz" to "Do not synchronise", click "Next page".

What you expect:

• You're going to continue to edit the question.

What actually happens:

• Error: mdb->get_record() found more than one record! errors are shown.

See http://moodle.org/mod/forum/discuss.php?d=195449
the
public function comment_on_datasetitems($qtypeobj, $questionid, $questiontext,
$answers, $data, $number) {
global $DB;
$comment = new stdClass();
$comment->stranswers = array();
$comment->outsidelimit = false;
$comment->answers = array();
// Find a default unit:
if (!empty($questionid) && $unit = $DB->get_record('question_numerical_units',
array('question' => $questionid, 'multiplier' => 1.0))) {
$unit = $unit->unit;
should use another $DB function call to allow for more than one record.