I found a (possible) bug in JMix:

If I click on the "Restrart" button, I get the following SQL Error:

Debug info: SELECT * FROM

WHERE id = ?
[array (
0 => 0,
)]
Error code: invalidrecord
Stack trace:
line 1390 of /lib/dml/moodle_database.php: dml_missing_record_exception thrown
line 1366 of /lib/dml/moodle_database.php: call to moodle_database->get_record_select()
line 37 of /mod/hotpot/attempt.php: call to moodle_database->get_record()

Moodle (Build: 20140117)Version 2013111801.01
User/System Language German