loadrunner_http _header_acceot

[问题描述]:
请求header中为：
-------------------------------------------------------------
Accept: */*
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返回包抓包如下：
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HTTP/1.1 200 OK
Server: nginx
Date: Tue, 28 Apr 2015 06:19:34 GMT
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 29
Connection: keep-alive

{"info":"?????","status":"y"}
----------------------------------------------------------

[解决如下]:
web_submit_data  add http header ：
web_add_auto_header("Accept", "application/json, text/javascript, */*; q=0.01");
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Accept:application/json, text/javascript, */*; q=0.01
-----------------------------------------
[next]
请求包头对比后发现没有做json格式说明，但为什么返回是charset=ISO-8859-1格式呢？