Iv6Addresses can have different States:
  enum State_e
  {
    TENTATIVE, /**< Address is tentative, no packet can be sent unless DAD finished */
    DEPRECATED, /**< Address is deprecated and should not be used */
    PREFERRED, /**< Preferred address */
    PERMANENT, /**< Permanent address */
    HOMEADDRESS, /**< Address is a HomeAddress */
    TENTATIVE_OPTIMISTIC, /**< Address is tentative but we are optimistic so we can send packet even if DAD is not yet finished */
    INVALID, /**< Invalid state (after a DAD failed) */
  };

The state transition is handled (i.e., an address starts at TENTATIVE_OPTIMISTIC, after the DAD is switched to PREFERRED, etc.).

The problems with the current implementation are:
1) Address state is not checked when the address is used, i.e., a node can use a DEPRECATED or INVALID address.
2) There is no fallback action when an address is marked as "to not be used". As a result, a node might not have any usable address.

This issue is partially related with the way the addresses are generated. Right now only a carefully built simulation might trigger this problem.
Nevertheless this might become an issue with the fd-netdevice.