django admin overwrites objects

[Jorge]

Hi , I think django has a problem in admin, I have a model like :

class Test(models.Model):

code_test= models.CharField(max_length=5,primary_key=True)
name = models.CharField(max_length=15)

when i get to admin and i make add a test fill the fields with for example code_test = a and name = first test. And them make save, until there no problem it saves. now I add another Test and the fields this time Code_teste = a and name = second test.

this time django OVERWRITES the older object, instead of saying that the object with that pk already exists. please tell help i have this problem in one produtive system.

Django version 1.1.1