When editing content in admin ui 2 you cannot save if an richtext field has a header with <br>'s

To reproduce:

Create a new article
Click in the 'intro' and type 'one'
Select 'Heading 1' from the toolbar
Press shift+enter
type 'two'
Press shift+enter
type 'three'
Click publish.

The content will not save and an error will be thrown.