ie7 jQuery.click only registers when target has background

.trigger
            {

            display : block ;
            width : 100% ;
            height : 100% ;
            z-index : 3 ;
            position : relative;
            /* BACKGROUND: #0f0; */
            cursor : pointer ;
            zoom:1;
            }

.trigger div
            {
            display : block ;
            background : #fff;  
            position : absolute ;       
            width : 48px;
            height : 48px ;
            left : 0px ;
            top : 0px ;

            filter:alpha(opacity=10);
            opacity : 0.1;          
            }

.trigger:hover div
            {
            filter:alpha(opacity=30);
            opacity : 0.3;  
            }

        $('.trigger').click(function(){
            //doIt
        })

<div id="wallItem218" class="wallItem" style="width: 48px; height: 48px; overflow: hidden; float: left; position: static; display: block;">
    <img class="thumb" src="http://bouwmaat.brandinteractive.nl/modules_media/wall/thumb/16.jpg" style="width: 4开发者_Go百科8px; height: 48px;">
    <img class="large" style="display: none; width: 48px; height: 48px;" src="http://bouwmaat.brandinteractive.nl/modules_media/wall/large/16.jpg"> 
    <div class="trigger" style="width: 48px; height: 48px; top: -48px; cursor: pointer;">
        <div></div>
    </div>
</div>

code is above. If i activate the background value on the .trigger, i can click the element to do something. If i remove the background, i can't click it anymore.

Any ideas?

Workaround: using transparent GIF image