Behavior of the Monitor of a Schedule object at turnaround:
Not an issue, behavior it's by design.
At the time of the turnaround a new monitor instance will be created.
The old monitor is frozen at this time, that means if a task is still in status "Active" the status of the task will not be updated once it ends. The task status in the monitor will remain the same that the task had a the time of turnaround.
The final status of the task can be viewed using the Statistic of the respective object.