We can still use one of the test servers and the user normally uses both and then releases them when done.
The "Review Sandbox" shows up when editing the web project setting. It's displayed in step 2 of the Edit Web Project Wizard where the Deployment Servers are set up/updated. There are several parameters displayed including Transport Name, Host, Port, URL, Type, Username, Source Path, Excludes, Target Name and Allocated. The "Review Sandbox" shows up beside allocated. Normally this has a user name and then in their sandbox, they can release the server(s). However, it shows "Review Sandbox" which, of course, does not correspond to a user.
I'm guessing this may have happened when submitting content to the live server. Don't know.