How to reproduce:
1. Create a post in the "Edit" view
2. Split the post somewhere in the middle
3. Change to "Source" view, notice it added <!--more-->
4. Change to "Preview" view
5. Change to "Source" view, notice it now says <div id='extendedEntryBreak' name='extendedEntryBreak'></div>
If the user clicks Publish without first going back to the Edit, it publishes the div rather than the comment.