That might be a typical example of bug, which in my case turns out to be useful :)
The fact is that, regarding task notifications, the manual states:
It is possible to provide assignees with notifications when a task is added to their list
That means that no mechanism is though for notify unassigned tasks (kind of funny for me...). Question is: is the reminder supposed to work only for assigned tasks as well (and that would be a bug)?
I think that the real "bug" is that notifications should not be sent ONLY when tasks are assigned...