Lightbox intermittent cropping issue

About to do a new version of our site and have been testing rtMedia on our development site. It’s looking pretty good so far but we have a basic problem. On some images, when the image is viewed with the lightbox, the image is cropped. On others it works perfectly. Images below to illustrate and also a link to the activity stream where you can see it going wrong for yourself. What do we need to resolve this as it would be a dealbreaker for us if we cannot fix it?

OK, I’m a new user so I cannot upload images. :frowning:

Here’s the link though.