M5 Cleanup: After switching tabs, the Xinha areas in a template turn into regular textareas

Start editing a document. Note the working Xinha areas.
Click on the "Browse" tab
Click on the editing tab that holds the document you were just editing
The Xinha areas are now gone, and existing content is shown in normal textareas (including HTML markup)

The same thing happened to me after a Save action in the editing tab (without switching tabs). I can't reproduce this, though.