Added try/finally

IPython/utils/traitlets.py

@@ -205,8 +205,10 b' class Connect(object):'
     @contextlib.contextmanager
     def _busy_updating(self):
         self.updating = True
-        yield
-        self.updating = False
+        try:
+            yield
+        finally:
+            self.updating = False
 
     def _update(self, name, old, new):
         if self.updating: