Gutenberg: Background flashes when editing italicized or bolded text

[gwwar]

Describe the bug

It's a bit subtle but when typing with bold or italicized options on, the text background will flash on keypress between white and gray. Ideally this we should not see this.

To Reproduce
Steps to reproduce the behavior:

1. Visit /post.php
2. Start typing in a paragraph block
3. Italicize or bold that text
4. With the formatting active (folks see a gray background) continue to type
5. After some keypresses, the text background appears to flash

Expected behavior
No visible background flashing. Background should remain gray until we exit that formatted text section.

Desktop (please complete the following information):

• OS: OSX
• Browser Chrome
• Version 71.0.3578.98

Additional context

• WP 5.0.2

[youknowriad]

Duplicate of #12978

[gwwar]

@youknowriad Do you mind reusing my gif for your summary? This bug is hard to explain without visuals

[youknowriad]

Sure added. Thanks