A quick follow up…
I cannot replicate what you are experiencing. Do you have a link to your site to this page where I can see this and look at the code to find out what might be happening?
I did a test on my local site with a post and an over-sized image of 2000 pixels wide and it does not break out like that and tried this in Chrome, IE, Firefox, Opera, and Safari, but still unable to see it like your screenshot does.
