Doctrine 2 flushes the wrong entity first - doctrine-orm

Question

I have this database design and in some instances Doctrine 2 makes the correct decisions in insert order and sometimes not
I have an automated import process that imports and updates data as the data provider changes it. The field item.something_happened_item_history_id is the new field that causes issues
When starting the import
Step 1. No data in the database and I create one item and one item_history, where item_history.item_id is the item.id and item.something_happened_item_history_id is null. Now I do Flush and Doctrine can figure it out that it needs to insert item before item_history. All is good.
Step 2. Now a new import comes in, and some of the data already exists in the database from the Step 1. But in the new import I actually have a new unique item. So what I do is that I create the item and item_history exactly as in Step 1. But for some reason during the Flush Doctrine thinks that item_history needs to be saved before the item. Which can't be done, because of not nullable foreign key reference on item_history.
I understand that Doctrine makes decisions based on foreign key references and the field something_happened_item_history_id is causing trouble. But it doesn't cause any trouble in the step 1. The problems occur when there is already some data in the database that is loaded into the entityManager.
I haven't been able to figure out how to manipulate Doctrine 2 so that it would always save the item before item_history.
Any ideas how to solve it?
As I really do not want to change my database design, because Doctrine 2 can't figure out the insert order.
Also it is not an option to do more Flushes, as there is a lot of data validation done before the data goes to the database. And I do not want any corrupt data in the database.
Best Regards,
Hendrik
EDIT: Doctrine 2 mapping
/**
* #Table(name="item", uniqueConstraints={#UniqueConstraint(name="uc_something_happened_item_history", columns={"something_happened_item_history_id"})})
**/
class Item
{
/** #Id #Column(name="id", type="integer", options={"unsigned":true}) #GeneratedValue **/
protected $id;
/**
* #OneToMany(targetEntity="ItemHistory", mappedBy="item")
**/
protected $itemHistories;
/**
* #OneToOne(targetEntity="ItemHistory")
* #JoinColumn(name="something_happened_item_history_id", referencedColumnName="id", nullable=true, unique=true)
**/
protected $somethingHappenedItemHistory;
}
/**
* #Table(name="item_history")
**/
class ItemHistory
{
/** #Id #Column(name="id", type="integer", options={"unsigned":true}) #GeneratedValue **/
protected $id;
/**
* #ManyToOne(targetEntity="Item", inversedBy="itemHistories")
* #JoinColumn(name="item_id", referencedColumnName="id", nullable=false)
**/
protected $item;
}

Answer 1

I haven't resolved the problem the way I wanted.
But by making the item_id nullable, then the Doctrine is able to finish the flush.
Data is also correct in the database.