Flush monitor messages after demonitoring.

src/syn_groups.erl

@@ -408,7 +408,7 @@ leave_on_node(GroupName, Pid) ->
             case find_processes_entry_by_pid(Pid) of
                 [Entry] ->
                     %% demonitor
-                    erlang:demonitor(Entry#syn_groups_table.monitor_ref);
+                    erlang:demonitor(Entry#syn_groups_table.monitor_ref, [flush]);
                 _ ->
                     ok
             end,

src/syn_registry.erl

@@ -411,7 +411,7 @@ unregister_on_node(Name) ->
 
         Entry when Entry#syn_registry_table.monitor_ref =/= undefined ->
             %% demonitor
-            erlang:demonitor(Entry#syn_registry_table.monitor_ref),
+            erlang:demonitor(Entry#syn_registry_table.monitor_ref, [flush]),
             %% remove from table
             remove_from_local_table(Name);