Yeah, you need to change ALL of the images that have a similar naming convention. If you have a save before you added them to the party, go with that one for now. there's 8 pictures. slimegirls_1 through till slimegirls_8.
Not sure about that error though. Just seems to be a drawing error. Which happens on occasion, I think it's cause a bunch of custom variables are attached to the individual stats themselves.
The next public version will be out in 2-3 weeks. So if you can hold off using the slimes till then....