Editor 2.0: Using Title format applies it to the entire section not just what is highlighted

1. In the editor, create a header and a paragraph like this.

This is title
This is the paragraph for the header.

2. Highlight "This is a title" and select Title 1
3. Save and view

Bug
"This is a title
This is the paragraph for the header" both get the header syntax applied instead of just the title.