Comment 6 for bug 1435283

OK - so I reproduced this on 1.23.2 - it happens in a very specific set of circumstances - four units have a second port allocated:

| 2f0e5d14-c830-4e29-bca9-d661b70a3b50 | juju-devel3-machine-12 | ACTIVE | - | Running | james-page_admin_net=10.5.19.99, 10.5.19.110 |
| 4d1a00f3-f6bd-4ed2-8db9-a01358d81beb | juju-devel3-machine-14 | ACTIVE | - | Running | james-page_admin_net=10.5.19.101, 10.5.19.112 |
| d99e5fb0-b35c-4ef8-8d16-8d424a23cc6b | juju-devel3-machine-15 | ACTIVE | - | Running | james-page_admin_net=10.5.19.102, 10.5.19.111 |
| 03b1db44-ef2d-42c1-9c5e-c58df08e5ecf | juju-devel3-machine-16 | ACTIVE | - | Running | james-page_admin_net=10.5.19.103, 10.5.19.113

only juju-devel3-machine-12 observed a change in unit private-address from juju - this was the only one that rolled over the 99->100 barrier.