I noticed a problem with the html_mail plugin, when using FCKeditor and the templates plugin: the templates plugin performs an insert of the old text along with the text coming from the template, instead of replacing the old text, or insering just the text from the template, with the effect that, if some text is already present in the compose windows when you insert the template, it is duplicated.
I enclose a tgz with the old version of the functions.php file, the new one and a diff file
old version of plugins/templates/functions.ph, new version and diff