Fwd: EOF Key NULL problem

Dear all,

for two days now I am bugged by a strange behaviour I never encountered 
before. The short version is, that I have two Entities, entA and entB, 
with a one-to-many relationship between them, that is, there is a 
'entb' to-one relationship in entA and a 'entas' to-many relationship 
in entB.

Now, whenever I fetch an instance of entB, say instB, and do the 
following (sligtly abbreviated):

instA = createAndInsertInstance( "entA" );
instA. setEntB( instB );
instB. addToEntA( instA );     (*)
saveChanges();

The result depends on whether line (*) is in the code or not.

WITH (*), I see a SQL string that contains a NULL value for the foreign 
key, whereas WITHOUT (*), everything works fine and the foreign key 
value is copied correctly from instB to instA.

This is independent from the foreign key being a class property or not.

Furthermore, even if I set my foreign key manually, it is completely 
ignored and the above-described behaviour remains (that is, the foreign 
key value that already was set in the instance is nullified somewhere 
on the way to the database).

Yes, I tried addToBothSidesOfRelationshipWithKey, but to no avail.

Any clue what it is I am doing wrong?

- Thomas