Editor with enterMode set to ENTER_DIV alters content on paste

[engineering-this]

Type of report

Bug

Provide detailed reproduction steps (if any).

1. Open SDK sample: https://ckeditor.com/docs/ckeditor4/latest/examples/enterkey.html
2. Pick Create a new <div> from select under When Enter is pressed:
3. Focus editor at the end of content, press Enter and type some text.
4. Select all.
5. Copy.
6. Paste

Expected result

Editor content looks like:

<div>This is some sample text.</div>

<div>New line.</div>

Actual result

There is an extra div wrapping whole editor content:

<div>
<div>This is some sample text.</div>

<div>New line.</div>
</div>

Other details

• Browser: …
• OS: …
• CKEditor version: …
• Installed CKEditor plugins: …

[msamsel]

Issue might be reproduce with insertHtml method.

1. Use editor in ENTER_DIV mode
2. Put selection in new line
3. Use editor.insertHtml( '<div>one</div><div>two</div>' )

Source of the problem is how we insert nodes.
Wrapping DIV, which allows on writing in editor, remains in editor. So when node is added to editor, selection is located directly in this div, not under the body.
https://github.com/ckeditor/ckeditor-dev/blob/1f365357c043a74e69ad21f32c829929d8610106/core/editable.js#L1899-L1906

This result in situation that we get additional div surrounded inserted content.