Dynamic content breaks on edit

Description

Dynamic content breaks if user edits after inserting dynamic content (from another page's properties) into the TinyMCE editor.

Steps to reproduce

1. Create an Alloy Sample site from Visual Studio
2. Upgrade to the specific product versions.
3. Start the site and log in as administrator.
4. Enable dynamic content for the [MainBody] field of the Product page type.
5. Edit any product page, for example, Alloy Plan.
6. Go to the All Properties view and the Content tab.
7. Insert a dynamic content in [Main Body], select type = "Page property", select Page = "Root Folder" and property = "Name". Note: This can only be produced with "Root Folder"; other Page Types do not have this problem.
8. Place the cursor at the beginning of the [Page Property] inserted, press Enter to enter a new line, then press Backspace to go back to the previous line.

Expected: The [Page Property] goes back to the previous line.
Actual: The [Page Property] breaks and gets duplicated to two dynamic contents.

Other problem included:
At step 6, if you press Enter, move the input cursor to the first position of the new line, and then press Backspace, the [Page Property] breaks and is rendered as a text block.

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