diff --git a/src/calibre/gui2/device.py b/src/calibre/gui2/device.py
index 378c585efb..0e18929d81 100644
--- a/src/calibre/gui2/device.py
+++ b/src/calibre/gui2/device.py
@@ -599,7 +599,10 @@ class Emailer(Thread): # {{{
 
     # }}}
 
-class DeviceGUI(object):
+class DeviceMixin(object):
+
+    def __init__(self):
+        self.db_book_uuid_cache = set()
 
     def dispatch_sync_event(self, dest, delete, specific):
         rows = self.library_view.selectionModel().selectedRows()
diff --git a/src/calibre/gui2/ui.py b/src/calibre/gui2/ui.py
index 29a09d6a1d..9ff30aa768 100644
--- a/src/calibre/gui2/ui.py
+++ b/src/calibre/gui2/ui.py
@@ -44,7 +44,7 @@ from calibre.gui2.dialogs.scheduler import Scheduler
 from calibre.gui2.update import CheckForUpdates
 from calibre.gui2.main_window import MainWindow
 from calibre.gui2.main_ui import Ui_MainWindow
-from calibre.gui2.device import DeviceManager, DeviceMenu, DeviceGUI, Emailer
+from calibre.gui2.device import DeviceManager, DeviceMenu, DeviceMixin, Emailer
 from calibre.gui2.jobs import JobManager, JobsDialog, JobsButton
 from calibre.gui2.dialogs.metadata_single import MetadataSingleDialog
 from calibre.gui2.dialogs.metadata_bulk import MetadataBulkDialog
@@ -105,7 +105,7 @@ class SystemTrayIcon(QSystemTrayIcon): # {{{
 
 # }}}
 
-class Main(MainWindow, Ui_MainWindow, DeviceGUI, ToolbarMixin,
+class Main(MainWindow, Ui_MainWindow, DeviceMixin, ToolbarMixin,
         TagBrowserMixin, CoverFlowMixin, LibraryViewMixin):
     'The main GUI'
 
@@ -228,6 +228,8 @@ class Main(MainWindow, Ui_MainWindow, DeviceGUI, ToolbarMixin,
         QObject.connect(self.advanced_search_button, SIGNAL('clicked(bool)'),
                 self.do_advanced_search)
 
+        DeviceMixin.__init__(self)
+
         ####################### Start spare job server ########################
         QTimer.singleShot(1000, self.add_spare_server)