pageContext.setAttribute() on imported JSPs

The JSP editor properly picks up attributes added in scriptlet code of the current JSP, but not from scriplet code in included JSPs.

This works fine (no editor warnings):

test1.jsp:
<%
     pageContext.setAttribute("flag", true);
%>
<c:out value="${flag}"/>




This produces a warning on ${flag}:

included.jsp:

<%
     pageContext.setAttribute("flag", true);
%>

test2.jsp:
<%@ include file="included.jsp" %>
<c:out value="${flag}"/>


Do I have something misconfigured?  I've tried to put <%--@elvariable id="flag"--%> in 'included.jsp' but it only works if it is in 'test2.jsp' as well.