Duplicate teaser inserted on edit after filefield paths has run

To reproduce, use a page whose contents start with a table or something else markup-heavy:

1. Upload a file in File Attachments
2. Create a link to the default file path in page contents
3. Save

Now, everything looks fine in the db and on the page view. Filefield paths has changed the path to the new location. Except: the teaser in the database ends on an open tag (this is luck of the draw and depends on the content, obviously.) Still not a problem, until...

4. Re-edit
5. Now, "Show Summary in Full View" is unchecked, and the teaser is now duplicated in the content.

I am using WYSIWYG with CKEditor. When I check in the database after save, I'm seeing the correct markup and the correct teaser, except as mentioned the teaser ends on an open tag. This seems to be the key to reproducing this bug: that open tag. When you edit the page filters close the tag, then Drupal thinks the teaser is different from the body and tries to insert a teaser. But because there is no teaser field, it just plunks the teaser markup in on top of the full body markup.

Seems to me the HTML filter isn't being run on save as a result of the filefield upload paths stuff, which results in the open tag.

Anybody know how to fix this?