Related Posts showing wrong thumbnail image

Hi, I’m using the Twenty Twelve theme.

The problem I’m experiencing is that the thumbnails of some related posts are showing the wrong image.

For example: http://www.daringgourmet.com/2013/02/04/mongolian-beef/

Scroll down to the related posts. The images for the Chinese Orange Chicken and the Kung Pao Chicken are one of the “prep” instruction pictures, not the first/main image of the post. I don’t know what determines when the correct picture shows versus when the wrong one shows, I do everything the same way each time. When I add a new recipe post I insert a picture in the the very top, then start adding text and more pictures to follow. Most of the of time the thumbnails pull the very first picture. But in some instances, like the examples above, it randomly pulls from other ones from within the middle of the post.

I don’t want to use the featured image option because of the layout.

I’ve searched through thread after thread to find a solution to this but no such luck.

Please help!

Thanks.