I don't know exactly how this error occurs, but I suspect it's the Rich Text Editor's fault.

Steps to reproduce:
1. Create a wiki page with the following contents in Wiki markup mode:

----
{anchor:top_of_page}

2. Preview it, see that the horizontal line is there, then save and see that the horizontal line is still there.
3. Edit the page, which leads to the RTE. Everything looks great.
4. Go to the preview tab. It shows the literal four dashes.
5. Go to wiki markup mode, and see that the newline is gone.

This is extremely annoying when you've got large pages with lots of content and you have to hunt down collapsed newlines to straighten things out.