It happens when you create a payroll and then at the end of the payroll you don't check the box to advance the payroll.  If you pay all of the employees, then the box is checked automatically. If you pay some of them, then it is not as the assumption is you may be returning to pay the other employees.  In this case you must assert you are done by checking the box.

Change the next payroll date for a payroll schedule by editing it.