Search for "DFB". You find packages. Hit #1 is "DFB++". Search for "DFB+". Same results. Now, search for "DFB++". No output. The basic Web template stuff shows up on the sides but there's no text in the center. Not even the customary "Nothing Found."/"I could not find any ebuild..."
The package search, like `emerge -sS`, is a regular expression. Since the + is a special character in regular expressions, you need to escape it if you mean the literal character DFB\+\+
