When you view/edit the task, there is a link in the upper left corner called 'View Task Audit Trail'. Clicking this should show all the status change events (and others) for this task and tell you who/when it was changed to 'Complete'.
It's possible that whoever the task was assigned to closed it via timesheet, My Tasks portlet, etc.
I have checked that Task Audit Trail details, but that shows the resource assigned to this task only closed it which is not the case in real because the resource himself reported this issue. Any idea how come a task gets closed without the resource assigned or PM's notice. One more thing, this happened multiple times, each time PM reopens it and allows the resource to report time again.
Am attaching the screenshot of the same. Please check that and let me know if you are aware of this kind of issue before.
It is possible for a resource to 'close' a task by reporting time against it without explicitly changing the percent complete.
For example, if the resource's task assignment is say 8 hrs and the resource logs 4 hrs, then the % complete will automatically change to 50%. Then, if the resource logs more time, greater than or equal to 4 hrs, the sum is now greater than or equal to the original 8 hr assignment so PPM considers the task 100% complete. If the resource saves this time without either manually editing either the % Complete or Est Remaining Effort fields the task will close out.
Satya,Hi. I have an idea: may be this possible if you have automaticli execution step in WF that are change work plan status. In this case in audit set user who press button to move request/project to execution step.