The example you gave is not working because the autolink prefix does not match the term prefix. This is expected behavior.
In addition the term must have more characters than defined in Options > VaultWiki: Wiki Links > Minimum Characters for Auto-Links.
For example, if this setting is 4, then a term of "DVD" would not be autolinked to the "DVD" article, no matter what its prefix is.
Since you have more non-prefixed articles that are visible to me, please provide a new example which shows unexpected behavior:
- The name of a forum that has the autolink prefix set to No Prefix
- A post in that forum where a term is not autolinked
- The term in that post that should be autolinked