Confluence 6.6.3 (recently updated from 5.10)
I have a user who cannot view or edit pages properly. He is an admin of his space, and when he views a page, he doesn't see the content:
Normal View Mode:

His View Mode:

Normal Edit Mode:

His Edit Mode:

His edit mode doesn't switch the URL over to "editpage.action?" when it is supposed to, but it is still trying to render as edit mode. When you send him the correct "editpage.action?" URL he is able to edit and save the page normally, but as soon as he clicks edit again he's back to seeing the buggy screens.