Completed and graded lesson activity was not protected against making new attempt to answer some questions. Affected versions are 2.9 to 2.9.1, 2.8 to 2.8.7, 2.7 to 2.7.9 and earlier unsupported versions. Upstream patch: https://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-50516
*** This bug has been marked as a duplicate of bug 1264861 ***