Does not show the first cell pylab plot

Hi all

I tried to plot using a revision of my ipython notebook ask follows:

https://github.com/kangwonlee/nmisp-20-interp/commit/d0b4cbb4760edaf9737e33a6ef6c2227a226f168

If you view the file, I tried to `import pylab` and `show()` in the first cell. When I select the cell and press Shift+Enter, the plot does not show up at first (as `In[1]`) but at the second time (as `In[2]`), it does.

In the following revision, as I splitted the `import pylab` line as the first cell, the plot in the second cell shows up without much problem:
https://github.com/kangwonlee/nmisp-20-interp/commit/1877621ffb693a612848cf664a2931589632d0a9

My `jupyter` version is 4.4.0.
```sh
$ jupyter --version
4.4.0
```

Let me know your opinion; is there a step that I missed? or do people usually try it differently?

Thanks for your attention.

KW

Start by reproducing the first-cell import pylab and show() sequence in the two linked notebook revisions using Jupyter Notebook 4.4.0, comparing the first and second executions. Trace the notebook's plot-display behavior and add or update a regression test if the repository provides one; done means the plot appears on the first execution.

Written by the indexing model from the issue text.