Please, follow with the included example test2.odb 
 
1) Create a new db (internal db engine)  
2) Create two tables (book, writer) as in the included example test2.odb 
3) Create the 1:n relation: writerId -> bookWriter  
4) Create a form and its subform with the wizard (fWriter) 
   The connected fields are writer.writerId (master), book.bookWriter (slave) 
5) Enter a new book record in the subform for the record writerId=1 (Giovanni 
Pascoli)  
  
The foreign key "book.bookWriter" does not default to writer.writerId=1, 
it defaults to 0. So the subform creates a new record that is not connected 
with the record displayed in the form. 
 
In MSAccess the foreign key defaults to the connected value from the form. 
I humbly think this would be the right choice. 
 
Or, did I lose something? (Thanks for OO.o 2, it's my daily tool!)