Why can I get properties of doctrine locked entity but can't set this entity to another

Question

I've got a question. I would like to understand why I can get properties from a pessimistic write locked entity doing this:

$string = $entity->getTitle();

but I can't make it:

$otherEntity->setEntity($entity);

It works with the pessimistic read lock mode but not in pessimistic write mode.

Does anybody know why I can read it in write mode but not set it to another entity?

Is there a way to fix it cause I can't change the mode for all the application?