MDL-28949 has now been integrated into 2.3 master. We need to decide whether we should be backporting this change to stable branches.
Duplicated course completion entries in database not handled correctly
I don't think we need an issue to make a decision. This can be the backport issue and either it will be done or not.
I'm closing this wont-fix as we've now come to the end of Moodle 2.2 general bugfix support. So this would only be back-ported if it was a security issue.