MU Install lost user's VIEW TAB under POSTS

I have a WPMU install (about 3 years old) that has had many issues throughout 2011.

One is that the VIEW TAB has gone missing for "some" users (HTML / VIEW) in the POSTS area of the Dashboard.

Does anyone know how to get this back? (Visual Editor is not disabled under Personal Options in DASHBOARD>USERS)

Example site with this issue: