On my MT4 install, attempting to post a comment returns "Premature end of script headers" errors from mt-comments.cgi.
I've re-uploaded mt-comments.cgi in ASCII mode and set its permissions to 755 (as well as doing this for all other files not in mt-static).
Other possible fixes?
Edit: I should note that the comment is posted and the page re-published correctly -- the user just isn't being returned to the updated page.