Spring JS partial request - session expired

Question

I'm using Spring JS (Spring WebFlow) to do ajax requests. E.g.:

<input type="submit" id="searchButton" name="_eventId_search" value="Find" onClick="wait(this.id)" />
<script type="text/javascript">
    Spring.addDecoration(new Spring.AjaxEventDecoration({
        elementId: "searchButton",
        formId: "searchModel",
        event: "onclick",
        params: {fragments: "content"}
    }));
</script>

Problem appears when HTTP session gets expired and Spring Security sends login page as partial response. I know, this issue affects all AJAX libraries but I cannot find anything about Spring JavaScript (Dojo). Do you have a (simple) solution?

Thanks a lot