Problem with JetPack Edit CSS - pulls entire Post content into editor

See the issue I initially [reported to JetPack.](https://github.com/Automattic/jetpack/issues/3784)
#### The Problem

It seems that with Babble AND JetPack activated at the same time, somehow Babble gets confused and pulls the entire Post content (from a Post I've assigned a custom class to an image in) into JetPack's custom CSS editor. When I edit the CSS (delete the Post content and add my custom CSS), it actually deletes the entire Post and saves my custom CSS in its place.

Reproduce the problem with Babble and JetPack activated together, focusing on JetPack's custom CSS editor and a post containing an image with a custom class. Trace why the editor receives the entire post and verify that editing CSS no longer replaces or deletes the post content.

Written by the indexing model from the issue text.