Steps to reproduce:

1. Create a document with syntax

   |(%%)(% class="content-wrapper" %)(((
   Content
   )))
   

2. Edit the document in the WYSIWYG editor, changing, e.g., "Content" to "Test Content".
3. Save the document.

Expected result:

The syntax is unchanged apart from the content of the group syntax and the class is still applied on the div element.

Actual result:

The syntax is now

|(% class="content-wrapper" %)
(((
Test Content
)))

and the class is on the table cell instead of the group syntax.