[web2py] MySQL constraints not updated but appended to old ones

[thodoris]

I have a field 

    Field('uUser2', db.auth_user, default=auth.user_id),

at some moment i added ondelete="CASCADE"

later i changed it to ondelete="NO ACTION"

but when i checked my db i had 

  KEY `rUser2__idx` (`ruser2`),
  CONSTRAINT `sounds_ibfk_1` FOREIGN KEY (`ruser`) REFERENCES `auth_user` 
(`id`) ON DELETE CASCADE,
  CONSTRAINT `sounds_ibfk_2` FOREIGN KEY (`ruser2`) REFERENCES `auth_user` 
(`id`) ON DELETE NO ACTION

So the old constrain should be removed but it doesn't. Is this the expected 
behaviour??