Please see the attached screenshot -- you'll see that in the breadcrumb nav across the top, the thread title includes the prefix but it doesn't render correctly. The word "News" is slighly below the line, and it outside the brackets, which come after, for whatever reason. It's supposed to show up as "[News]". It shows up correctly everywhere else.
In the Thread Prefix Manager in ACP, I use the Rich Text field and supply the following input: