If a schedule has already been published in the future, and then a manager approves time off, Time Simplicity will move a single scheduled shift to Open Shift automatically. If the employee has two shifts scheduled on that day, however, Time Simplicity will only move one of the shifts to Open, and it leaves the second shift still assigned. A manager then needs to manually move the second shift to the Open Shift row.
This seems linked to the fact that a second shift creates a second row for the employee on the scheduler, but the Time Off request only populates a single row (not multiple).