User Field with zoho.loginuser

User Field with zoho.loginuser

I have a main form with User field that is populated with zoho.loginuser upon add.  As an admin, when I change the user field to another user, I want my subform to reflect the same loginuser.  The subform has a field called User_name and it is a string field (not a user field).

In the On Update of the User field in the Main Form, I wrote a deluge script to populate the User_Name field (string) of the subform so they are in synch.  

It does not appear that the functionality is present for User fields?  It does not work?

Does anyone have a workaround?

Thanks for any help!

Edith