I recently started using the WordPress plugin Smush.it which optimizes images for better user performance. Instead of slowing down page downloads with large-but-resized images, Smush.it trims the fat so you download less. For some reason, Smush.it intermittently conflicts with CloudFlare, often times giving errors or timing out.
If you’re getting this behavior, be sure to check out this thread of possible fixes. There are some workarounds listed, and I’m going through them now.