telepathy-gabble-0.13.6 (at least), doesn't unref current Sugar activity while unrefing all activities previously announced by a contact in extract_activities() function. The issue can be reproduced the by the following top-level Sugar usecase:

(1) client A shares new Sugar activity;
(2) client B joins it;
(3) client A reflects on appearing B and sets B's current activity to the newly shared one;
(4) client A leaves the channel;
(5) client B leaves the channel;
(6) on client A side, the refcount incremented by (3) is not reverted.

The affected code:

> --- a/src/conn-olpc.c
> +++ b/src/conn-olpc.c
> @@ -730,6 +730,7 @@ extract_activities (GabbleConnection *conn,
> 
>    if (old_activities != NULL)
>      {
> +      g_hash_table_remove (conn->olpc_current_act, GUINT_TO_POINTER (sender));
>        /* We decrement the refcount (and free if needed) all the
>         * activities previously announced by this contact. */
>        tp_handle_set_foreach (old_activities,