Unity MonoBehaviour seems to have another scope

Question

I have a class (EnemyBehaviour) which extends MonoBehaviour, this class has the following two methods:

    private Enemy enemy;

    public void set(Enemy enemy)
    {
        this.enemy = enemy;
    }

    public Enemy get()
    {
        return this.enemy;
    }

This class also has the unity method:

    public void Update()
    {
        Debug.Log(this.enemy);
    }

This method always prints Null.

But, If I call the get() method outside the self MonoBehaviour it returns the right instance.

    var eb = enemy.getGameObject().GetComponent<EnemyBehaviour>();
    Debug.Log(eb.get()); // it returns UnityEngine.Debug:Log(Object)

The Enemy class is a class which encapsulates the EnemyBehaviour.

public class Enemy
{
    private GameObject gameObject;
...

Then, I don't understand why inside the Update(), Start(), OnMouseDown(), or any "Unity method" the enemy property is Null. But if I access the property outside these methods (enemy.getGameObject().GetComponent().get()) it works.

I suspect that Unity MonoBehavour has it's own scope and the GetComponent() other scope.

Another strange thing is if instead of storing the "Enemy" class inside the Behaviour I store a string or Vector3, it works like a charm.

Any idea? Thanks

Edit:

Simplification of the problem: I have an Empty Game Object (Kernel) which instantiates all the other game objects, this has a Kernel class which extends the MonoBehaviour:

    public void Start()
    {
        var enemyGameObject = Resources.Load<GameObject>("Prefab/Enemy");
        var enemyBehaviour = enemyGameObject.transform.GetComponent<EnemyBehaviour>();
        var foo = new Foo();
        enemyBehaviour.Foo = foo;
        Instantiate(enemyGameObject);
        Debug.Log(enemyBehaviour.Foo); // OK, This one works
    }

Foo is a dummy class.

public class Foo
{
}

EnemyBehaviour just does:

public class EnemyBehaviour : MonoBehaviour
{
    public Foo Foo;

    public void OnMouseDown()
    {
        Debug.Log(Foo); // When I click on the GameObject, prints Null, it's not working
    }

Strange thing: If I replace the var foo = new Foo(); by var foo new Vector3(5,5,5); (Including chaning the type in EnemyBehaviour of course (public Foo Foo; -> public Vector3 Foo;)) everything works fine :S

Edit 2:

Found the issue, was related with the prefab, I was setting the Foo to the Prefab instead of the instance, Fix:

        var instance = Instantiate(enemyGameObject);
        var enemyBehaviour = instance.transform.GetComponent<EnemyBehaviour>();

Answer 1

The problem was related with the prefab, I was setting the Foo to the Prefab instead of the instance, Fix:

    var instance = Instantiate(enemyGameObject);
    var enemyBehaviour = instance.transform.GetComponent<EnemyBehaviour>();