Continuing the discussion from Display code blocks:
The solution combining FixedPre and Fred’s TinyMCE works, except for one thing. HTML tags are not displayed. If you again open the TinyMCE code editor, the code is in fact there, and using the browser’s element inspector also shows the code. Logging out of Fred and viewing the page also displays the code as expected.
This isn’t a complete disaster, since you can open TinyMCE’s code browser, but it’s still rather alarming to see the blank code block.