diff --git a/src/mcedit2/editorapp.py b/src/mcedit2/editorapp.py
index d543225..6d4bee6 100644
--- a/src/mcedit2/editorapp.py
+++ b/src/mcedit2/editorapp.py
@@ -589,12 +589,14 @@ class MCEditApp(QtGui.QApplication):
             for menu in previousSession.menus:
                 menuBar.removeAction(menu.menuAction())
 
-        if session is not None:
+        if session is None:
+            self.undoGroup.setActiveStack(None)
+        else:
             self.undoGroup.setActiveStack(session.undoStack)
 
             log.info("Adding session menus: %s", session.menus)
             for menu in session.menus:
-                menuBar.insertMenu(self.mainWindow.menuWindow.menuAction(), menu)
+                menuBar.insertAction(self.mainWindow.menuWindow.menuAction(), menu.menuAction())
 
             for action in session.topToolbarActions:
                 if action is None:
@@ -719,6 +721,8 @@ class MCEditApp(QtGui.QApplication):
                 self.undoGroup.removeStack(session.undoStack)
                 self.sessions.remove(session)
                 session.dealloc()
+                del tab
+                del session
                 gc.collect()
         else:
             self.tabWidget.removeTab(index)
diff --git a/src/mcedit2/editorsession.py b/src/mcedit2/editorsession.py
index f3bf27f..00a7bcf 100644
--- a/src/mcedit2/editorsession.py
+++ b/src/mcedit2/editorsession.py
@@ -547,9 +547,6 @@ class EditorSession(QtCore.QObject):
         self.worldEditor.close()
         self.worldEditor = None
 
-        # Break all reference cycles just to be absolutely sure.
-        self.__dict__.clear()
-
     def _updateVersionsAndResourcePacks(self):
         self.mcVersionMapper = QtCore.QSignalMapper()
         self.mcVersionMapper.mapped[str].connect(self.changeMCVersion)
diff --git a/src/mcedit2/widgets/block_replacement_list.py b/src/mcedit2/widgets/block_replacement_list.py
index 1465695..4ab53ed 100644
--- a/src/mcedit2/widgets/block_replacement_list.py
+++ b/src/mcedit2/widgets/block_replacement_list.py
@@ -19,7 +19,7 @@ class BlockReplacementButton(QtGui.QWidget):
         super(BlockReplacementButton, self).__init__()
 
         self.replacementList = BlockReplacementList()
-        self.replacementDialog = QtGui.QDialog(QtGui.qApp.mainWindow)
+        self.replacementDialog = QtGui.QDialog()
 
         self.replacementOk = QtGui.QPushButton(self.tr("OK"))
         self.replacementOk.clicked.connect(self.replacementDialog.accept)