Wp-calypso: Editor: Clicking Save when drafting a post prevents the preview from refreshing

[jblz]

Steps to reproduce

1. Starting at URL: https://wordpress.com/post
2. Select a test site (if your test user has more than one)
3. Enter some content and click preview
4. Close the preview modal
5. Change the post content
6. Click the Save link / button:
   
7. Click preview

What I expected

The draft to be saved & the preview to show the updated content

What happened instead

The draft doesn't appear to have saved & the preview shows the previous content (it doesn't appear the iframe reloads)

Browser / OS version

Chrome 59, MacOS Sierra

[mattsherman]

Here's a screen cap that illustrates the issue (I too hit this today)...