It's hard to find a cause in PHP after it's published but I tried. I can see that both images have different styles and names. First guess would be some kind of plugin conflict. You can check this by turning the plugins off one by one. Refresh your browser and look for changes. This way of working can't do any harm.
When you're not able to solve it by configuring the plugin, you could try to use a style hack by placing the second or first image way out of canvas with margin-top: -2000px; for example. Try it with and without possition: absolute;
I tried it myself using firebug on the post-image style but that didn't work.
That's all I can do for you. Good luck solving it!