C# insertion of a record with CurrencyManager AddNew() method during the insertion of a father table

[polocar]

Hi,
I have noticed a strange behaviour of CurrencyManager objects in C# (I
use Visual Studio 2005 Professional Edition).
Suppose that you have a SQL Server database with 2 tables called
"Cities" and "Persons", and that:
"Cities" has 2 fields called "IDCity" and "NameCity"
"Persons" has 3 fields called "IDPerson", "NamePerson" and
"IDCityAddress"
with "IDCity" and "IDCityAddress" fields relationed with the
classical father-child relation (the value for "IDCityAddress" is
required, you can't set it to null).
Suppose to define 2 DataTable objects called "dtCities" and
"dtPersons" (bound to the 2 tables), and 2 CurrencyManager objects
in this way:
cmCities = (CurrencyManager)BindingContext[dtCities];
cmPersons = (CurrencyManager)BindingContext[dtPersons,
"Cities_Persons"];
(where "Cities_Persons" is the relation that binds "IDCity" of
"dtCities" to "IDCityAddress" of "dtPersons").
Now, think to insert a new city with the statement:
cmCities.AddNew();
and, before confirming the "dtCities" record insertion with the
cmCities.EndCurrentEdit() statement, insert a new person with the
statement:
cmPersons.AddNew();
(of course in the C# form there will be some TextBox controls bound to
the various fields of the 2 current records of the tables).
Ok, now you can't confirm the "dtPersons" record insertion with
the cmPersons.EndCurrentEdit() statement before confirming the
"dtCities" record insertion (the "IDCityAddress" value is
required in "dtPersons", and that value doesn't exist yet in the
"IDCity" field of "dtCities"), so you must necessarily give
this order to the statements:
cmCities.EndCurrentEdit();
cmPersons.EndCurrentEdit();
but when the first statement is executed, cmPersons.Position is set to
-1, and the "dtPersons" new record isn't saved in
"dtPersons".
This behaviour doesn't happen if I add a "dtPerson" record during
the modify of a "dtCities" record (cmPersons remains set to its
value and the cmPersons.EndCurrentEdit() statement saves the new record
correctly, adding it to the table).

Can you explain me why??? Is there a way to insert a person during the
insertion of a city without being forced to introduce other additional
code?

Thank you very much