PyCharm community version 2016.3, when I enable Vim Emulator and open an Ipython Notebook, it just does not work. I believe it is very easy to duplicate, and I don't know if that is a bug for PyCharm or there are settings to solve the issue.
Checking submitted issues for Pycharm on the Jetbrains site reveals the following:
In a cell, insert mode is activated by default. Unfortunately, Esc is trapped by the IDE because it is needed for IDE actions. Fortunately, pressing Ctrl+C as in the original VIM will cancel insert mode and place you in "command line" mode.