Dynamic content breaks on edit

Description

Dynamic content breaks if user doing edit after insert dynamic content (from other page's properties) to TinyMCE editor.

Product versions:
EPiServer.CMS.UI 8.3.0
EPiServer.CMS.Core 8.8.2

Steps to reproduce
1. Create an alloy sample site from visual studio and upgrade to the specific product versions.
2. Start the site and log-in as Administrator.
3. Enable dynamic content for [MainBody] field of Product page type.
4. Edit any product page (Alloy Plan for example). Go to All Properties page and Content tab.
5. Insert a dynamic content in [Main Body], select type = "Page property", select Page = "Root Folder" and property = "Name" (please note that this can only be produced with "Root Folder", other Page Types do not have this problem).
6. Now place the input cursor at the beginning of the [Page Property] inserted, press "enter" to enter new line, then press "backspace" to go back to the previous line.

Expected: The [Page Property] go back to the previous line.

Actual: The [Page Property] broke and got duplicated to two dynamic contents.

Other problem included:
At step 6, if you press "enter" and then moved the input cursor to the first position of the new line, then press "backspace", the [Page Property] breaks and being rendered as a text block.

Typing at the position immediately behind the [Page Property] also cause it to break and rendered as a text block.