Featured Images Do Not Crop (Thumbnails/Slider)

Hi, I've got a new install of Simple Catch here at: http://jensbaking.thewingedheart.com/ Everything is looking lovely so far, but I'm having trouble getting my existing featured images to display properly as thumbnails and slider images. My thumbnails don't get cropped to a square. They are just re-sized and have white space to the right or below depending on if they are portrait or landscape. Similarly, slider images get re-sized down to the height constraint of the slider rather than being cropped at full size to the slider dimensions. I have tried running the Regenerate Thumbnails plugin several times, and it appears to run successfully, but there is no change. Note that if I upload a new image and set it as the featured image, the problem does not persist (this is the case with "Test Post"). Any insight would be lovely. Another plugin to update my thumbnails, perhaps? Thank you!