个人觉得这个地方也没有必要转义，也不会去转义

import com.alibaba.fastjson.JSONObject;

public class Demo {
    public static void main(String[] args) {
        JSONObject json = new JSONObject();
        json.put("key", "content\tvalue");
        System.out.println(json.get("key"));
        // result:content	value
    }
}

刚刚试了一下可以啊，\t转成制表符了

\t should not be converted to a tab. Tabs are not allowed inside strings.

The JSON Data Interchange Syntax says: Insignificant whitespace is allowed before or after any token. Whitespace is any sequence of one or more of the following code points: character tabulation (U+0009), line feed (U+000A), carriage return (U+000D), and space (U+0020). Whitespace is not allowed within any token, except that space is allowed in strings.

This issue has been fixed and can be closed. It's escaping tabs correctly
Tested both \t and \u0009 on version 1.2.75