Cluster binding change results in config-changed hook error

This is slightly a corner case, however when the unit's cluster binding is getting updated into a different network space with the "juju bind" command, the config-changed hook is failing with the following stack trace:

unit-memcached-0: 14:26:42 DEBUG unit.memcached/0.config-changed active
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed Traceback (most recent call last):
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/config-changed", line 384, in <module>
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed main()
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/config-changed", line 378, in main
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed hooks.execute(sys.argv)
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/charmhelpers/core/hookenv.py", line 731, in execute
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed self._hooks[hook_name]()
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/charmhelpers/core/host.py", line 637, in wrapped_f
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed restart_functions)
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/charmhelpers/core/host.py", line 659, in restart_on_change_helper
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed r = lambda_f()
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/charmhelpers/core/host.py", line 636, in <lambda>
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed (lambda: f(*args, **kwargs)), restart_map, stopstart,
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/config-changed", line 274, in config_changed
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed update_status()
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/config-changed", line 352, in update_status
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed if replication.get_current_replica():
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed File "/var/lib/juju/agents/unit-memcached-0/charm/hooks/replication.py", line 61, in get_current_replica
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed log("Current replica value: %s" % replica, level="INFO")
unit-memcached-0: 14:26:42 WARNING unit.memcached/0.config-changed TypeError: not all arguments converted during string formatting
unit-memcached-0: 14:26:42 ERROR juju.worker.uniter.operation hook "config-changed" (via explicit, bespoke hook script) failed: exit status

Memcached is keeping the cluster ip values from the former network space in the /var/run/repcached_replica file:
$ juju run -a memcached "cat /var/run/repcached_replica; echo"
- Stdout: |
    10.99.43.67,10.99.43.119
  UnitId: memcached/0
- Stdout: |
    10.99.43.67,10.99.43.119
  UnitId: memcached/1

and the charm cannot decide about the master and secondary roles, as the cluster ip address from the new network space, won't match the ips stored in repcached_replica:

def get_current_replica():
    replica = get_repcached_replica()

    if replica:
        master, secondary = replica
        ip_addr = get_relation_ip('cluster')
        if ip_addr == master:
            replica = secondary
        elif ip_addr == secondary:
            replica = master

Workaround: update the repcached_replica content on each memcached unit using the unit ip addresses from the new network space:

identify ip addresses of the cluster binding:
$ juju run -a memcached "network-get --primary-address cluster"
- Stdout: |
    10.99.40.102
  UnitId: memcached/0
- Stdout: |
    10.99.40.156
  UnitId: memcached/1

upgrade the content of the /var/run/repcached_replica
$ juju run -a memcached 'echo -n "10.99.40.102,10.99.40.156" | tee /var/run/repcached_replica'

Resolve the units:
$ juju resolve memcached/0
$ juju resolve memcached/1