I have seen this issue a couple of times now but can figure out why it's happening. If I create a new post and upload 5 or 6 images that I will be using for the article, insert the images and then realise that one of them needs editing, the old image that was removed keeps coming back (slightly warped) even though I have selected the new edited version.
This still happens if I delete all the images from the post, as well as the post itself and start again. I have cleared the cache, but the problem persists. The only way around this is to complete the steps above, rename the image and create a new post.
I am running the latest version of WP (3.5.1) with the Genesis framework and News Child theme.