Automatically sort unsceduled periods

Go to 'Settings | Miscellaneous | Timetable'. There is a new box you can tick: 'Always sort unscheduled periods'.

If you change the place of a period on the right hand side of the timetable (or if a period is scheduled or unscheduled), the unscheduled periods are automatically sorted anew. This feature helps you to not 'lose' any periods and to easily keep track.