sync completed tasks with RTM

I expected to see a completed task from RTM, but the new completed task
wasn't sync at all as if there were no new task.

Even if I create a new task and complete it before syncing with RTM (RTM
doesn't know about this task before I complete it), this task should be
synced with RTM. I don't want to just throw away completed tasks because I
want to keep track of what I've done both in Atrid and RTM. So it should
be able to sync completed tasks with RTM.