If Compact Strings is disabled, the StringBuffer/StringBuilder(CharSequence)
constructor truncates the string in half, eg:
        StringBuffer sb2 = new StringBuffer((CharSequence)new StringBuffer("test2"));
        System.out.println(sb2);
        System.out.println(sb2.toString().equals("test2"));

Results in output ==>
    tes
    false

JDK13 regression from change JDK-8218227