Teaserbreak moving problem

In my problem, the teaserbreak is replaced with a fakeobject. The fakeobject can be generated by those steps:
- Create a text: <p>P1</p><p>P2</p><!-- break--> (the teaserbreak (without space) is inserted then the cursor is at the end of the second paragraph).
- Move the teaser break to after the first paragraph. The expected result is:
<p>P1</p><!-- break--><p>P2</p>
But the result is:
<p>P1</p><img align="" alt="Unknown Object" src="../../sites/all/libraries/ckeditor/images/spacer.gif?t=A8LE4JO" /><p>P2</p>

Tested with Mac OS 10.5, Firefox 3.6.9. I was about to post at #924714: Incorrect behavior when adding template without replacing content but then realized that was another problem.