If I want to edit a post that was had initially set "using HTML", all the HTML tags appear afterwards
in clear text as if UBB changed the post to "using BBCode"; furthermore when editing I don't have
the choice of changing this setting. The quick-and-dirty solution was to:
1. copy-and-paste to a text editor the text given by UBB including the HTML tags
2. delete the post
3. re-add the post with cut-and-paste from the text editor, then make the changes and submit

That's not quite convenient, isn't it ?