How to force Doctrine 2 not to load the entire collection when adding?

Question

Doctrine ORM

There are two entities Account and Operation.
The account contains the history of transactions. (one-to-many relationship)
The relationship is declared as EXTRA_LAZY.
Why is it that when adding a new operation to the collection ($this->operations->add($operation) , the add method of PersistentCollection) is it fully loaded (up to 100000 entries can be in one account)?