posts disappear when saved as draft

If I publish a post, then go back in post.php and change the status to draft, and then save, the post disappears from my blog and from edit.php. No way to get it back. Also, it doesn’t get listed in the “your drafts” list. What to do? I’m not so much concerned about getting any particular post back. I’m just concerned about the logic of the program. Doesn’t seem like changing status to draft and saving should cause a post to disappear.