Post/Preview buttons don't work when commenting in wiki markup mode in Internet Explorer with ISO-8859-1

Trying to comment on a page on Internet Explorer 6 in the wiki markup tab (whether it is the default or not) doesn't work. The Post and preview buttons don't do anything when clicked.

This only occurs when ISO-8859-1 has been set as the character encoding for Confluence. If it is UTF-8, saving works.

This seems to be independent of the database encoding (it was originally uncovered on an instance with the DB encoding set to latin1).
It also seems to be independent of the browser encoding setting.

Switching to rich text mode allows the user to comment.
FireFox 1.5 doesn't seem to suffer from the same problem.