jupyter notebook echos on launch: [IPKernelApp] ERROR | UNKNOWN MESSAGE TYPE: 'comm_open' #1

$ jupyter notebook
[I 15:01:50.759 NotebookApp] Serving notebooks from local directory: xxx
[I 15:01:50.759 NotebookApp] 0 active kernels 
[I 15:01:50.759 NotebookApp] The IPython Notebook is running at: http://localhost:8888/
[I 15:01:50.759 NotebookApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[I 15:01:58.130 NotebookApp] Creating new notebook in 
[I 15:01:58.621 NotebookApp] Kernel started: bbd50554-8a71-4227-9291-73bb6e954f36
java version "1.9.0-ea"
Java(TM) SE Runtime Environment (build 1.9.0-ea-b82)
Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-ea-b82, mixed mode)
[IPKernelApp] ERROR | UNKNOWN MESSAGE TYPE: 'comm_open'