Updating a Single Simple Discussion Forum causes the first edited posting to be deleted

I have attached an mp4 movie (1.7MB, no sound) of this 'bug' in action. Please let me know if you want to see the movie in a different format,

When creating a Single Simple Discussion Forum, the teacher first has to write in some text in the 'Forum introduction' text box. Note that this text appears both on the Forums index page (http://demo.moodle.org/mod/forum/index.php?id=2), and as the first posting of the new forum. Ideally the text describing this new forum on the index page should just be a few words. However, the text in the first posting will probably be longer, perhaps containing a detailed explanation of the task.

So, to add an explanation of the task, a teacher will click on the 'edit' link at the bottom of the first posting and type an explanation. So far so good. after saving, the original brief explanation of the new Forum added in the 'Forum introduction' remains unchanged, and the longer explanation appears as expected.

However, on clicking on the [Update this Forum] button, and making any necessary changes (or no changes) and then clicking on the [Save changes] button. The longer explanation in the first posting disappears, and reverts back to the original text typed in the 'Forum introduction' text box.

The only 'solution' at the moment to this bug is to be aware of it, and save a copy of the first posting on ones hard disk in case the forum needs to be updated.