After adding a Reference, the ForeignKeys in the DB are not updatet

After query a record from the DB, where a foreign key is null, and changing only the reference belonging to this foreign key, and only these reference no other value of the record, a save of the record doesn't lead to a change in the foreign key field.

For example: I'll save a user record with some data of a regestration and give him the possibillity to add a city where he cames from later in his account settings, if no other user attribute is changed, the state of the user record is still CLEAN. The result is that I can access the user->City property correctly only as long as no refresh from the db is done. So the changing of the foreign key belonging to the city isn't persistent in the DB.

Example Code:
$user = new Model_User();
$user->firstName = md5(rand());
$user->save();

$id = $user->id;
unset($user);
assert(! $user);

$user = Model_UserTable::getInstance()->find($id);
assert(!$user->relatedExists('City'));

$user->City->name = 'Mainz';
$user->save();
unset($user);

$user = Model_UserTable::getInstance()->find($id);
$user->refresh(true);
assert($user->City->name == 'Mainz');

The last assert failse. I realized the problem while updating just a referenz using the fromArray() method like $user->City->fromArray(). The city would be saved correctly in DB but the foreign key in the user table would not be updated. After debugging I recognized that the $user is not replaced in UnitOfWork::saveGraph() because the $user is still in CLEAN state.

Using " $user->coreSetRelated('Country', $user->Country);" or "$user->state(Doctrine_Record::STATE_DIRTY);" after "$user->City->name = 'Mainz'" would fix the prob in this case. As well as creating a new City instance an set $user->City with this instance like:

$city = new Model_City();
$city->name = 'Mainz';
$user->City = $city;

Also $user->isModified(true) is true. So I fixed the issues in my case by changing the state of my records to DIRTY if the "$this->state() == CLEAN && $user->isModified(true) == true" in the preSave() method of an abstract class that my Base classes are extending....