This case should only occur when the coordinator is started and before it has the chance to bootstrap tasks, a worker completes a task it was assigned. The RTR doesn't really do anything about these tasks until it has some knowledge of them (i.e. after the coordinator bootstraps it may notice a task it just got has already been completed. Instead of running the task again it will just run the callback). If however, the coordinator doesn't bootstrap correctly we may get "dangling" tasks. That is, a worker may announce it has completed a task that never gets cleaned up by the RTR. I don't think these situations should occur unless the coordinator fails to bootstrap correctly.