webkit: strong turns into b after deletion

[Sergiy Kuzmenko]

Steps to reproduce

^ represents caret position:

1. Make a text bold. The resulting markup will be something like <strong>a</strong>^.
2. Press backspace/delete. Markup becomes ^ (strong node gets deleted).
3. Type something. Markup becomes <b>a</b>.

Expected result

I would expect one of the following:

1. strong rather than b (since this is the default markup).
2. no formatting (since b node was removed).

Actual result

strong gets replaced with b.

Other details (browser, OS, CKEditor version, installed plugins)

Webkit browsers on OSX.

[Jakub Ś]

After some checking it has turned out this is a duplicate of #13224.