I have exactly this same problem. In fact, this is the second time I’ve hit it, on two separate WordPress installations. See https://zahambie.com/blog/2008/06/30/ownership-issues/ for details of the first time, which was fixed by (bizarrely) using only the visual editor.
This current incarnation of the bug is not proving as easily beaten.
Does anyone out there have any idea what’s happening and how to fix it.