This issue was reported by Art Fiedler via nashorn-dev openjdk alias:

http://mail.openjdk.java.net/pipermail/nashorn-dev/2016-November/006662.html

email content cut-pasted here for convenience:

--- email from Art Fiedler ----

When calling the following code, I expected the call to myJSObject inside
testJSOCall to pass the current
scope as a ScriptObjectMirror to JSObjectImpl's call method as the thiz
argument. In this case without
modifying the call to myJSObject() should 'this' automatically be passed to
the call() method?

Thanks,
Arthur Fiedler

public class NashornBugTest
{
    public static void main(String[] args) throws Exception {
        NashornScriptEngineFactory factory = new
NashornScriptEngineFactory();
        ScriptEngine scriptEngine = factory.getScriptEngine();
        scriptEngine.put("myJSObject", new JSObjectImpl());
        scriptEngine.eval(
            "var a = 42;\n" +
            "function testJSOCall(b) {\n" +
            "    myJSObject('text purposely did not pass b');\n" +
            "}\n" +
            "testJSOCall(a);\n");
    }
    public static class JSObjectImpl extends AbstractJSObject
    {
        @Override
        public Object call(Object thiz, Object... args)
        {
            if (ScriptObjectMirror.isUndefined(thiz) || thiz == null)
                throw new IllegalArgumentException("'thiz' is
undefined/null");
            // TODO: need the value of 'b' in the calling function
            return super.call(thiz, args);
        }
        @Override
        public boolean isFunction()
        {
            return true;
        }
    }
}