Projected Date recalculation.
If there are Tasks with Predecessor relationship the Projected Date recalculation is done the following way when adding an Actual Completion Date to one of them:
For example, we have Task A, Task B and Task C, where Task B is Task A's successor, and Task C is Task B's successor. If Actual Completion Date is added to Task A, the Projected Completion Date will be recalculated automatically for Task B (provided the Project Settings Update Type is set to Automatic and On Change), but it will not be recalculated for Task C, as currently the system calculates the Projected Completion Date for one level up and down of the updated Task i.e for the successor and the predecessor of the updated Task. This is designed for the performance reasons.
To recalculate the Projected as well as other dates for all the Tasks you can either refresh the page or use the Recalculate Timeline option from the Project Actions.