如何阻止弹出窗口隐藏在IE中的嵌入对象后面

Question

要重现问题，请在pdf前移动pupup并尝试调整其大小。在IE（在8和9上测试）弹出部分隐藏在pdf背后。在Firefox和Chrome中一切正常。

<h:body>
        <h:form>
            <iframe id="overviewFrame" src="http://docs.jboss.org/richfaces/latest_3_3_X/en/devguide/pdf/richfaces_reference.pdf" width="900" height="800" />          
            <h:commandButton value="openPopupWithPdf">
                <rich:componentControl target="pdfPopup" operation="show" />
            </h:commandButton>
        </h:form>
        <h:form>
            <rich:popupPanel autosized="false" id="pdfPopup" resizeable="true" width="300" height="100" moveable="true" overlapEmbedObjects="true">
                <f:facet name="controls">
                    <a4j:commandLink id="documentHideEditLink" styleClass="hidelink" onclick="#{rich:component('pdfPopup')}.hide()" execute="@this">
                        <h:graphicImage value="/img/modal/close.png" />
                    </a4j:commandLink>
                </f:facet>
                <f:facet name="header">
                    This is popup header
                </f:facet>   
                <h:panelGrid>
                    Some text
                </h:panelGrid>
            </rich:popupPanel>
        </h:form>
    </h:body>

如果我使用a4j：mediaOutput而不是iframe。