Delete task performs a 'soft' delete on regular, active tasks, i.e. the task status is changed to 'Deleted'.
The task is still available to view by displaying status 'Deleted'.
If you delete a task while in 'Deleted' it will be deleted permanently.
In order to permanently remove all 'softly' deleted tasks, please go to File/Maintenance and do Purge Deleted Tasks.
Archived tasks can be deleted from the Completed Report and are deleted permanently (after a warning).