I noticed it on a downloaded version, but I've just checked your online demo, and it has the same problem.

When you click on an HTML document, the edit window does not display correctly.

The "Save" and "Save As" buttons are there, as is the input field for the filename, but the textarea and the form elements below that are not shown.

There is no error message displayed however.

Plain text, Perl scripts and files with no extension display correctly though (if they contain text).