Pressing power button causes a blank figure

还没有人认领这个 Issue。

Pressing the power button (toggle interaction) causes the whole figure to become blank, instead of just disabling interaction. Difficult to reproduce this every time. Tried with both Firefox and Chrome, and in some cases (mostly Firefox), the button worked as intended. In some cases the plot line is still visible, but the axes and labels disappear.

Tested on jupyter lab. My versions are the following:

```
matplotlib 2.2.2 py36_1 conda-forge
ipympl 0.2.1 py36_0 conda-forge
jupyter_client 5.2.3 py_1 conda-forge
jupyter_core 4.4.0 py_0 conda-forge
jupyterlab 0.32.1 py36_0 conda-forge
jupyterlab_launcher 0.10.5 py36_0 conda-forge
@jupyter-widgets/jupyterlab-manager
@jupyter-widgets/jupyterlab-manager v0.35.0 enabled OK
Firefox 61.0.1
Chrome 67.0.3396.99
```

首先，使用列出的 Firefox 和 Chrome 版本在 JupyterLab 中复现电源按钮切换，然后比较绘图变为空白的情况与正常工作的情况。完成的标准是，禁用交互后绘图线、坐标轴和标签仍然可见，而不是使图形变为空白或部分隐藏。

由索引模型根据 Issue 内容生成。