You need to add the render attribute to your ajax tag. It defaults to 'none'. @this should probably fix your situation.
<f:ajax render="@this" listener="..." />
http://www.jsftoolbox.com/documentation/help/12-TagReference/core/f_ajax.html
edit: @this is most likely not what your looking for, but instead @form or the container id where the list you sort is located.