Issue Overview

I have a page with a number of different Heading blocks. Some of the blocks display fine on the front-end (e.g. <h3>Some text</h3>) and other headings have an extra <br> tag included (e.g. <h3>Some text<br></h3>)

These couple of headings are displaying fine

This heading has the extra <br> tag

When you look at the block with the extra tag, in the Visual Editor, it appears fine. If I click in the block and try to remove any extra (invisible) characters from the end, I can't.

If I switch to the Code Editor, I can see the extra <br> tag which I never put in and I can't remove (using the Visual Editor).

Steps to Reproduce (for bugs)

1. Insert multiple headings and update page
2. View markup on front-end and see if any include extraneous tags

Expected Behavior

Headers shouldn't randomly include <br> tags

Current Behavior

Headers randomly include extra markup that you can't get rid of

Gutenberg 2.5.0
Firefox Quantum 59.0.2 (64-bit)
WP 4.9.4