When summary/parent tasks in the Gantt are edited in the timeline the duration of the parent task is not always consistent with the net duration of its children.
Please review this Screen capture for the described behavior: https://www.screencast.com/t/la1PzVZaYc
This issue can be avoided, if the duration of the parent tasks can be configured to be fixed. Then the parent task's duration will only be dependant on the duration of its children.
Furthermore the timeframe of the parent task would be editable by changing the starting date.