This is based on a hack I use to reverse a default AHA T0-Do assignment behavior.
Create a Reviewer account name "Unassigned".
Create a NEW Personal Setting "Default To-Do Assignment:"
Change the Default To-Do Assignment from my self to "Unassigned"
Then when I create to-dos they are assigned to the dummy account "Unassigned" Until I want to assign them
This has been fixed by new To Do auto assignment behavior.