=== modified file 'landscape/broker/client.py'
--- landscape/broker/client.py	2013-07-25 13:54:29 +0000
+++ landscape/broker/client.py	2016-01-13 10:23:21 +0000
@@ -1,6 +1,6 @@
 from logging import info, exception
 
-from twisted.internet.defer import maybeDeferred
+from twisted.internet.defer import maybeDeferred, succeed
 
 from landscape.log import format_object
 from landscape.lib.twisted_util import gather_results
@@ -67,7 +67,7 @@
         """
         if not (scopes is None or self.scope in scopes):
             # This resynchronize event is out of scope for us. Do nothing
-            return
+            return succeed(None)
 
         # Because the broker will drop session IDs already associated to scope
         # of the resynchronisation, it isn't safe to send messages until the

=== modified file 'landscape/monitor/usermonitor.py'
--- landscape/monitor/usermonitor.py	2016-01-11 18:34:49 +0000
+++ landscape/monitor/usermonitor.py	2016-01-13 10:29:55 +0000
@@ -39,10 +39,14 @@
             self._publisher.stop()
             self._publisher = None
 
-    def _reset(self):
+    def _resynchronize(self, scopes=None):
         """Reset user and group data."""
-        super(UserMonitor, self)._reset()
-        return self._run_detect_changes()
+        deferred = super(UserMonitor, self)._resynchronize(scopes=scopes)
+        # Wait for the superclass' asynchronous _resynchronize method to
+        # complete, so we have a new session ID at hand and we can craft a
+        # valid message (l.broker.client.BrokerClientPlugin._resynchronize).
+        deferred.addCallback(lambda _: self._run_detect_changes())
+        return deferred
 
     @remote
     def detect_changes(self, operation_id=None):