Featured Cat Slider image sizes

On my Asian travel blog at http://www.travelnasia.com I current have 6 posts being featured using the Featured Cat Slider in the Slider area. All the featured images for these posts are 800x533px, but for some reason the slider insists on trimming 2 or 3 of them back to 800x445px which looks really odd. Can you advise why it’s not honouring the image file sizes and how to fix that?