In a Nintex form in New mode, I am defaulting a field to "Current User" however that user can select a different person in the field.  Field type is a Person/Group field. 

The scenario in which this occurs is entering a leave request on behalf of another staff person.  Form defaults to the currents user (me) but I can select a member of my team (Jane Doe).  During the approval cycle, a follow up request data task occurs.  In these subsequent Request Data tasks, this field is reset to the default (current user), overriding the manual entry made in the first step.   How can I prevent this behavior?  I'd prefer not to create a task form for every task.  I'd like it to default in New Mode but store the value and not reset to the default in edit mode.

Any advice is appreciated.