After upgrading to 1.9 (from 1.7, passing through 1.8), we suddenly got duplicated IP addresses in managed hosts.
For example, from 1.7:

mysql> select * from nics where ip='10.0.30.219';
+-------+-------------------+--------------+-----------+------+---------+-----------+-----------+-----------------------------------------------------------------------------------------------------------------+---------------------+---------------------+----------+----------+----------+---------+------+------------+-----+-------------+---------+------------+------------------+--------------+
| id    | mac               | ip           | type      | name | host_id | subnet_id | domain_id | attrs                                                                                                           | created_at          | updated_at          | provider | username | password | virtual | link | identifier | tag | attached_to | managed | mode       | attached_devices | bond_options |
+-------+-------------------+--------------+-----------+------+---------+-----------+-----------+-----------------------------------------------------------------------------------------------------------------+---------------------+---------------------+----------+----------+----------+---------+------+------------+-----+-------------+---------+------------+------------------+--------------+
| 24293 | 44:a8:42:14:79:71 | 10.0.30.219 | Nic::Bond | NULL |    9633 |      NULL |      NULL | --- !ruby/hash:ActiveSupport::HashWithIndifferentAccess
network: 10.0.30.0
mtu: '1500'
netmask: 255.255.254.0
 | 2015-07-27 12:30:27 | 2015-11-11 07:32:55 | NULL     | NULL     | NULL     |       1 |    1 | bond0      |     |             |       0 | balance-rr |                  |              |
+-------+-------------------+--------------+-----------+------+---------+-----------+-----------+-----------------------------------------------------------------------------------------------------------------+---------------------+---------------------+----------+----------+----------+---------+------+------------+-----+-------------+---------+------------+------------------+--------------+
1 row in set (0.01 sec)

After the upgrade:

mysql> select * from nics where ip='10.0.30.219';

+-------+-------------------+--------------+--------------+------------------------+---------+-----------+-----------+-----------------------------------------------------------------------------------------------------------------+---------------------+---------------------+----------+----------+----------+---------+------+------------+-----+-------------+---------+------------+------------------+--------------+---------+-----------+--------------------+
| id    | mac               | ip           | type         | name                   | host_id | subnet_id | domain_id | attrs                                                                                                           | created_at          | updated_at          | provider | username | password | virtual | link | identifier | tag | attached_to | managed | mode       | attached_devices | bond_options | primary | provision | compute_attributes |
+-------+-------------------+--------------+--------------+------------------------+---------+-----------+-----------+-----------------------------------------------------------------------------------------------------------------+---------------------+---------------------+----------+----------+----------+---------+------+------------+-----+-------------+---------+------------+------------------+--------------+---------+-----------+--------------------+
| 24293 | 44:a8:42:14:79:71 | 10.0.30.219 | Nic::Bond    | NULL                   |    9633 |      NULL |      NULL | --- !ruby/hash:ActiveSupport::HashWithIndifferentAccess
network: 10.0.30.0
mtu: '1500'
netmask: 255.255.254.0
 | 2015-07-27 12:30:27 | 2015-11-03 08:02:46 | NULL     | NULL     | NULL     |       1 |    1 | bond0      |     |             |       0 | balance-rr |                  |              |       0 |         0 | NULL               |
| 31234 | 44:a8:42:14:79:71 | 10.0.30.219 | Nic::Managed | data120.example.domain |    9633 |        11 |        11 | NULL                                                                                                            | 2015-11-03 11:54:37 | 2015-11-03 11:54:37 | NULL     | NULL     | NULL     |       0 |    1 | eth0       |     |             |       1 | balance-rr |                  |              |       1 |         1 | NULL               |
+-------+-------------------+--------------+--------------+------------------------+---------+-----------+-----------+-----------------------------------------------------------------------------------------------------------------+---------------------+---------------------+----------+----------+----------+---------+------+------------+-----+-------------+---------+------------+------------------+--------------+---------+-----------+--------------------+
2 rows in set (0.02 sec)

mysql> 

This of course fails the uniq validation ("Ip has been, thus preventing the removal of the duplicate NIC.

This seems a bit like the issue mentioned here:
https://groups.google.com/forum/#!topic/foreman-users/7i3xCfgb8Xk

ignore_puppet_facts_for_provisioning is set to "true".