tooncher/controls.py: added ref to TODO

tooncher/controls.py

@@ -135,6 +135,7 @@ class ExtendedControls:
 
     def _handle_xevent(self, xevent):
         # TODO investigate why some release events get lost
+        # https://stackoverflow.com/q/18160792/5894777
         if isinstance(xevent, Xlib.protocol.event.KeyPress) \
                 or isinstance(xevent, Xlib.protocol.event.KeyRelease):
             self._handle_xkeyevent(xevent)