The Task completion checkbox must be unchecked or Progress set to 0% before the Activity can be set to Canceled. The Task will then be deleted and there are no track on actually performed tasks on the canceled activity.
The core functionality of deleting tasks is more suitable for Deleting a Project Activity than cancel of an activity when looking at an option to cancel a started activity.
Test Scenarios:
1. Create a project activity, set to status approved
2. add a task with checkbox Completed set on the activity
3. add a task with a progress between 0% and 100% on the activity
4. Change status on the activity to Canceled (RMB/Status from the activity head)
5. Verify, not possible to cancel activity due to task progress >0%
-> Need to change task progress to 0% before Activity can be canceled and then all tasks are deleted -> No track on already performed work.
Should It be possible to cancel an activity where you have reported progress on tasks ?