Doctrine ORM, two different querys produce the same result set

Question

I'm using Doctrine 1.2 and Symfony 1.4.

In my action, I have two different query that return different result set. Somehow the second query seem to change the result (or the reference?) of the first one and I don't have any clue why..

Here is an example:

  $this->categories = Doctrine_Query::create()
       ->from('Categorie AS c')
       ->innerJoin('c.Activite AS a')
       ->where('a.archive = ?', false)
       ->execute();

  print_r($this->categories->toArray()); // Return $this->categories results, normal behavior.

  $this->evil_query = Doctrine_Query::create()
       ->from('Categorie AS c')
       ->innerJoin('c.Activite AS a')
       ->where('a.archive = ?', true)
       ->execute();

  print_r($this->categories->toArray()); // The result is now changed it return $this->evil_query results instead!

Why Doctrine behave this way ? It's totally driving me crazy. Thanks!