Simple bug, reproduced on multiple PC's so I won't post hardware specs, all PC's running Windows XP SP2 + all updates.
Bug: If you select the second file or playlist icon (second one down from the top) in Preferences>File Types menu, it will not display in Windows Explorer when it is set in "List" or "Details" view.
Instead, explorer will display the old school Winamp blue wave file type icon for both files and playlists. Seems like a Winamp registry bug since this problem was reproduced on multiple PC's. Remember this is only for "List" or "Details" views in Explorer, not "Thumbnails" or any other.