If I could add something here to help you out (and John while he's busy elsewhere), the first thing that springs to mind with a list is the default padding - if there is padding on the <li> element then the image dimensions inside will be skewed.
Anyway, I took this inkling into the Chrome dev console and, sure enough, the padding on the <li> is to blame - in the "style.css" file;
Code:
.art-postcontent ul>li, .art-post ul>li, .art-textblock ul>li
{
padding-left: 15px;
}
zero/remove this padding and that should fix things with the dimensions and also showing the last image.
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