Placing a Create Task module and synchronizing it to a unit will also display the task creation notification.
The Created option in the Set Task State module serves the same purpose, so the Create Task module should not display that notification.

Only tasks created on mission start with Create Task will not display the notification.

It would also probably be a good idea to prevent the Create Task module from displaying created tasks on the tasks list, and let Set Task State - Created do it instead.
This way, Create Task would only be used to "manage" tasks, not to effectively create them.