Don't keep aspect ratio with jQuery resizable while holding shift

I'm resizing a div with jQuery resizable and I only want to resize its height.

I managed to only resize while dragging bottom helper :

$('div').resizable({
   handles: 's',
});

But if I hold shift key, width is changing. See http://jsfiddle.net/6p20qjmr/3/

How can I disable this behavior?

Edit: The div container width may change after initial resizable call.

Solution

I find a way to achieve what I want using resize parameter and reseting width after every resize event:

$(".resize").resizable({
    handles: 's',
    resize: function() {
        $(this).css('width', '');
    }
});