Jetpack. By far my favorite plugin for WordPress. So many great features, all rolled into one. It’s pretty damned awesome.
At least it was pretty damned awesome, until WordPress v3.5 was released. Then it was demoted to just ok. It started causing issues with embedded Youtube videos, tossing up some really ugly PHP error messages on the post that had video embedded.
To keep a long story short, you can read all of the details over at the support site. 28 posts later, we have arrived at this post. I actually helped to fix a a major WordPress Plugin. This pleases me.
The shorter version is that there is a plugin out there that is causing issues related to featured images in posts. Actually, it was the lack of a featured image that was causing the issue. The fix is in the post linked up, if you are having the same issue, but I can answer any questions you might have in the comments!