Validation failed on initial autosave of new notebook

[efiring]

I made a fresh notebook to test the mpl notebook backend (mpl master) and ipympl. After verifying that the notebook backend is still non-functional with mpl master (no plot appears), I switched browser windows, and when I came back I found that the autosave operation had triggered a validation warning:

Notebook validation failed: {'model_id': '4da0a9266d91445e97058ad725d230c7'} is not valid under any of the given schemas:
{
 "model_id": "4da0a9266d91445e97058ad725d230c7"
}

A similar test with ipympl also triggered the same form of warning upon autosave and save via clicking the notebook disk icon. This is after running, so a plot was displayed.

I am using recent packages installed via conda:

# packages in environment at /Users/efiring/anaconda/envs/test:
#
jupyter                   1.0.0                    py35_0    conda-forge
jupyter_client            4.4.0                    py35_0
jupyter_console           5.0.0                    py35_0
jupyter_core              4.2.1                    py35_0
(test) efiring@manini2:~$ conda list ipython-notebook
# packages in environment at /Users/efiring/anaconda/envs/test:
#
ipython-notebook          4.0.4                    py35_0

and matplotlib master 2.0.2.post4458+gc38205a51.
The test notebook is this:

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "#%matplotlib notebook\n",
    "import ipympl\n",
    "import matplotlib.pyplot as plt\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import matplotlib\n",
    "print(matplotlib.__version__)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "fig, ax = plt.subplots()\n",
    "ax.plot([1,2,3,2,1])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "plt.show()\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "anaconda-cloud": {},
  "kernelspec": {
   "display_name": "Python [conda env:test]",
   "language": "python",
   "name": "conda-env-test-py"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.5.2"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 1
}

(I initially opened this in the ipython repo; I have copied it over from there and closed the original.)