In the admin section, under Networking => Peers. When I have chosen a peer, if I go to the services tab and change some of the checkboxes, upon save I get notices like:

Notice: Trying to get property of non-object in /var/www/mahara/admin/mnet/mnet_services.php on line 60

I had set up a Mahara peer, although I don't think the type of peer matters.

The offending line is:

} elseif ($host2service->publish != $publish || $host2service->subscribe != $subscribe) {

$host2service is defined on line 47:

$host2service = get_record('mnet_host2service', 'hostid', $_POST['hostid'], 'serviceid', $key);

The following psql output might help:

moodle-mahara=# \d mdl_mnet_host2service
Table "public.mdl_mnet_host2service"
Column | Type | Modifiers
-------------------------------------------------------------------------------------
id | bigint | not null default nextval('mdl_mnet_host2service_id_seq'::regclass)
hostid | bigint | not null default 0
serviceid | bigint | not null default 0
publish | smallint | not null default 0
subscribe | smallint | not null default 0
Indexes:
"mdl_mnethost_id2_pk" PRIMARY KEY, btree (id)
"mdl_mnethost_hosser_uix" UNIQUE, btree (hostid, serviceid)

moodle-mahara=# select * from mdl_mnet_host2service;
id | hostid | serviceid | publish | subscribe
-----------------------------------
1 | 3 | 1 | 0 | 1
2 | 3 | 2 | 1 | 0
(2 rows)