The images should be saved once the are initially loaded. Unlike the weather app, I never force any images to reload themselves in the comics app. Have you tried exiting out of the app and going back in? (Silly question I know, but sometimes failed images load for me when I restart boxee.)
Where is your location (country/state/city) currently?
Can you attach me a new copy of your boxee.log? I should be able to tell what it's doing to the images in terms of loading then.