Tinymce: Backspace fails to delete after element with contenteditable="false"

[trepmal]

New ticket based on #1385

If attempting to use the backspace key to delete content that appears after an element with contenteditable="false", it fails to delete but does move the caret.

Example:

With this content:

<div contenteditable="false">not this</div>
a b c d e

If I select a b c d e and hit backspace, the caret moves and the content is not deleted. The delete key (aka forward-delete) works fine.

Reproduced on www.tinymce.com which appears to be at v 4.5.5 as of this post.

Tested in Chrome (v 58.0.3029.33 beta) and Firefox (v 52.0.1) on macOS (v 10.12.3)

Notably, this issue surfaces in WordPress, since oEmbed items are wrapped in a contenteditable="true" div in the _Visual_ editor.

[metricjs]

Replicated on OSX Chrome in Wordpress and www.tinymce.com, and on Windows 7 Chrome and Firefox in www.tinymce.com. Replication might be dependent on how content is added to the editor, or something related.

[systemx-xx]

It would seem it works the same way if the content editable is behind some text for example
Hello<br><div contenteditable="false">world</div>
When you try and backspace before the word world to remove the line break it does not work. The caret moves but it does not remove the line break.

[GouTong-dandan]

For the contenteditable="false" node, which does not contain text, svg path element in this case, the backspace will skip the svg, and delete the text before that if the user continues clicking backspace.
OS: Android phone

https://user-images.githubusercontent.com/79293925/108654575-f0c92d80-7503-11eb-8b80-f398d0af55cc.mp4