Cursoring broken when widgets inside an empty par

Issue details

As above.

Steps to reproduce

https://quick-phone.glitch.me/

The widgets are absolutely positioned to show where they are but the bug is the same when they are not absolutely positioned.

Cursor at the end of the heading, press Enter, cursor position does not change. Continue to cursor up and down through the empty spaces into the heading and lower par and you'll see oddly positioned cursors. This is worse in Firefox.

ProseMirror version

Latest in Glitch

Affected platforms

• Chrome
• Firefox - untested
• Internet Explorer
• Other