referrer_charset is a lie. It's really the user's default_charset.

chrome/browser/download/download_util.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Download utility implementation
 
 #include "chrome/browser/download/download_util.h"
 
 #if defined(OS_WIN)
 #include <shobjidl.h>
@@ skipping 140 matching lines @@
   return (download_path == desktop_dir);
 }
 
 void GenerateFileNameFromRequest(const DownloadItem& download_item,
                                  FilePath* generated_name) {
   std::string default_file_name(
       l10n_util::GetStringUTF8(IDS_DEFAULT_DOWNLOAD_FILENAME));
 
   *generated_name = net::GenerateFileName(download_item.GetURL(),
                                           download_item.GetContentDisposition(),
-                                          download_item.GetReferrerCharset(),
+                                          download_item.GetDefaultCharset(),
                                           download_item.GetSuggestedFilename(),
                                           download_item.GetMimeType(),
                                           default_file_name);
 }
 
 // Download progress painting --------------------------------------------------
 
 // Common bitmaps used for download progress animations. We load them once the
 // first time we do a progress paint, then reuse them as they are always the
 // same.
@@ skipping 457 matching lines @@
                               kMaxShelfSize);
   }
 }
 
 void RecordDownloadCount(ChromeDownloadCountTypes type) {
   UMA_HISTOGRAM_ENUMERATION(
       "Download.CountsChrome", type, DOWNLOAD_COUNT_TYPES_LAST_ENTRY);
 }
 
 }  // namespace download_util