Performance 'Complete' Task doesn't allow entry of a Reason?

Summary

Performance 'Complete' Task doesn't allow entry of a Reason?

Content

Every year, for those employees who are on leave of absence at the end of the performance cycle, we acknowledge their documents on their behalf, so that all documents are completed.  In the classic UI, we did this by using the Move Task Forward function, and when using Move Task Forward (or Back), you have the ability to enter a reason for moving the task.  And we created a reason for use for this specific scenario.

We just discovered that in the responsive UI, in order to acknowledge on behalf of the employees on LOA, that we have to use the Complete task.  The Move Task Forward function is not available to select when you're on the last task of the process flow.  However the Complete task just immediately/automatically completes the document without allowing the entry of a Reason code.