I encountered the same problem and found a temporary solution:
1. Open the following file:
2. Lines 121, 122, and 123 contain the value "1000". This IF statement is checking the width in pixels of the original image and executing functions based on this information. Change the "1000" to a value larger than the biggest image you would like to use in your slideshow. (For example, I'm using images 1280x984 in my slider, so I changed "1000" to "2000" just to be safe). Make sure you change all 3 instances of "1000".
I'm not a js / php expert, but the code seems to written in a way to keep the "cropping image" and the preview image in the wp-admin area to a certain width for screen viewing purposes (at least, that's how it should work). However, when an image > 1000px is used in the slider, the code breaks down.
Let me know how it turns out.