Steps to reproduce

CSP-54743 (restricted to public) provided a video on how to reproduce this bug: confluence.avi.zip

1. Create a Page
2. In Rich-Text Editor, insert the following

   a
   b
   c
   

3. Select 'c'
4. Choose 'Panel' from Text Effect drop-down
5. Select 'c' within Panel
6. Choose 'Preformatted' from Text Effect drop-down.
7. Boom! All text are gone and only 'c' left with just one style applied
8. Switching to wiki-markup editor or preview would not load

The same behaviour applies to Panel, Preformatted (noformat), Quote, Code text effect.

Workaround

Apply the Text Effect through macro browser instead of choosing them from the drop-down