Toggle visibility with jQuery is immediately collapsing

Question

I am a beginner in jQuery and JavaScript. I have the following problem: Every time I try to open an div area it is immediately collapsing. The HTML is:

<ul class="information"><li><a class="opener" href="#">opener</a> <div class="slide-block"> ...

The JavaScript:

jQuery(".information .opener").on("click", function(event){

        var opener = jQuery(this);

        // Show/hide the content by toggling active class
        opener.parent().find(".slide-block").slideToggle("fast",function(){
            opener.parent().toggleClass("active");
        });

        //  Return false to subdue the click
        return false;

    });

In think it has to do with an upgrade of jQuery...

Thanks in advance

Julius