oracle的编码问题

我安装oracle9i的时候就选的UTF-8字符集；
已经将注册表里的NLS_LANG设成：AMERICAN_AMERICA.UTF8;
然后将NLS_NCHAR_CHARACTER(国家字符集)也改成了UTF8(此疑问一：安装oracle9i的时候没有选择国家字符集的选项)；
然后在sql plus中存入一条含中文的数据，
再在plsql（已设置为UTF8）中编辑该条数据时提示：一个或多个UTF8字段包含非UTF8数据编辑时可能出现意外结果。
我找不到原因了，字符集和国家字符集我都设成了UTF8了
在sql plus sheet中查询select * from nls_session_parameters（客户端字符集），结果如下：
PARAMETER                                                                                  VALUE
------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------
NLS_LANGUAGE                                                                               AMERICAN
NLS_TERRITORY                                                                              AMERICA
NLS_CURRENCY                                                                               $
NLS_ISO_CURRENCY                                                                           AMERICA
NLS_NUMERIC_CHARACTERS                                                                     .,
NLS_CALENDAR                                                                               GREGORIAN
NLS_DATE_FORMAT                                                                            DD-MON-RR
NLS_DATE_LANGUAGE                                                                          AMERICAN
NLS_SORT                                                                                   BINARY
NLS_TIME_FORMAT                                                                            HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT                                                                       DD-MON-RR HH.MI.SSXFF AM
NLS_TIME_TZ_FORMAT                                                                         HH.MI.SSXFF AM TZR
NLS_TIMESTAMP_TZ_FORMAT                                                                    DD-MON-RR HH.MI.SSXFF AM TZR
NLS_DUAL_CURRENCY                                                                          $
NLS_COMP                                                                                   BINARY
NLS_LENGTH_SEMANTICS                                                                       BYTE
NLS_NCHAR_CONV_EXCP                                                                        FALSE
查询select * from nls_database_parameters（服务器字符集）
PARAMETER                      VALUE
------------------------------ ------------------------------------------------------------------------------------------------------------------------
NLS_LANGUAGE                   AMERICAN
NLS_TERRITORY                  AMERICA
NLS_CURRENCY                   $
NLS_ISO_CURRENCY               AMERICA
NLS_NUMERIC_CHARACTERS         .,
NLS_CHARACTERSET               UTF8
NLS_CALENDAR                   GREGORIAN
NLS_DATE_FORMAT                DD-MON-RR
NLS_DATE_LANGUAGE              AMERICAN
NLS_SORT                       BINARY
NLS_TIME_FORMAT                HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT           DD-MON-RR HH.MI.SSXFF AM
NLS_TIME_TZ_FORMAT             HH.MI.SSXFF AM TZR
NLS_TIMESTAMP_TZ_FORMAT        DD-MON-RR HH.MI.SSXFF AM TZR
NLS_DUAL_CURRENCY              $
NLS_COMP                       BINARY
NLS_LENGTH_SEMANTICS           BYTE
NLS_NCHAR_CONV_EXCP            FALSE
NLS_NCHAR_CHARACTERSET         UTF8
NLS_RDBMS_VERSION              9.2.0.1.0
请大家帮帮忙解决这个问题啊，谢谢啦！