When using an icecore:refresh tag on a page that has an ace:tabSet, which uses a showEffect, the showEffect is fired on each refresh interval.

Sample code:
    <h:body>
        <icecore:refresh interval="1"/>
        <h:form id="iceForm">
            <ace:tabSet id="testTabSet"
                        showEffect="clip">
                <ace:tabPane label="Tab One">
                    <h:outputText value="Tab One Content"/>
                </ace:tabPane>
                <ace:tabPane label="Tab Two">
                    <h:outputText value="Tab Two Content"/>
                </ace:tabPane>
                <ace:tabPane label="Tab Three">
                    <h:outputText value="Tab Three Content"/>
                </ace:tabPane>
            </ace:tabSet>
        </h:form>
    </h:body>

Each time the refresh happens, the clip effect is fired. This issue is not seen on the ICEfaces 3 code base. This might effect other components that render animations as well.