Content added after PDF Viewer macro is deleted when saving the page from WYSIWYG editor

Steps to reproduce:

1. Make sure the default editor is set to CKEditor
2. Install PDF Viewer Macro 1.6.1
3. Create a new page
4. Attach a PDF file to it
5. Add the PDF Viewer macro
6. Go to Source
7. Add some text content after the PDF macro -> 1. png
8. Go back to the WYSIWYG view mode: the text is properly displayed inside CKEditor -> 2.png
9. Save & View: the text has disappeared -> 3.png
10. Edit the page and check both views (WYSIWYG & Source): the text is not displayed -> 4.png + 5.png
11. Check the History tab: the deletion of the content doesn't appear in the diff -> history.png

The bug doesn't reproduce on the other editors: Wiki, GWT.