Overlay doesn’t fit image on article post…or vice versa

Loving the Renkon theme so far! I’ve encountered a new bug and couldn’t find any other posts in the support forum relating to it, so here goes. On my test site (http://adamcornwell.com/renkon/) I have an article post with a featured image (the art gallery one). For some reason, Renkon is forcing the image to be square (it’s actually rectangle like the rest) while the overlay is rectangular as it should be and overhangs on the right hand side of the image. I’ve seen one or two other Renkon websites with this issue, but your demo site doesn’t have this problem. Any thoughts? Is this already being worked on for the forthcoming update? Thanks Ellen!

Cheers,
Adam