getContentDispositionFilename uses encodedFilename in both parameters where decoded one should be used

[mimkorn]

/**
 * Returns the filename formatted for inclusion in a Content-Disposition
 * header. Includes both a plain version of the name and a UTF-8 version
 *
 * @since 7.4.8
 * @param filename
 *            The filename to include
 * @return A value for inclusion in a Content-Disposition header
 */
public static String getContentDispositionFilename(String filename) {
    String encodedFilename = EncodeUtil.rfc5987Encode(filename);

    return String.format("filename=\"%s\"; filename*=utf-8''%s",
            encodedFilename, encodedFilename);

Observe that you use encodedFilename in both cases instead of using filename in one case and encodedFilename in the other.