Restoring Moodle 1.9 backup file into Moodle 2.1 removes all Enrolment methods

To reproduce this problem, do the following: 1. Created a blank course and assign a user to it with teacher privileges, 2. Restore a Moodle 1.9 backup file, 3. In step '2. Destination' of the restoring process select "Delete the content of this course and then restore" option, 4. In step '5. Review', an error message should come up saying "error/restore_problems_processing_questions" After that this user would not be able to access that course any more. You can use the Admin account to access that course and do the following: 5. Check the 'Enrolled users', and you will see that there are no users, 6. Check the 'Enrolment method', and you will see that all enrolment methods are disabled.