TIdMultiPartFormDataStream TIDHTTP的参数有关问题

TIdMultiPartFormDataStream TIDHTTP的参数问题？
代码如下，利用TIDHTTP和TIdMultiPartFormDataStream post参数

para = “aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa”；
TIdMultiPartFormDataStream *stream = new TIdMultiPartFormDataStream();

try{
stream->AddFormField("method",method);
stream->AddFormField("timestamp",timestampStr);
stream->AddFormField("para",para);

stream->Position = 0;
IdAntiFreeze1->OnlyWhenIdle = false;
IdHTTP1->Request->ContentType = "multipart/form-data";
IdHTTP1->Post("http://127.0.0.1//index.php",stream));

}__finally{
delete stream;
}
利用抓包工具查看，发现自动添加了“=”（70个自己就添加一个）
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa=
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa=
aaaaaaaaaaa

------解决方案--------------------
多加两个参数试试：

stream->AddFormField("para", para, "iso-8859-1", "8bit");