I think I remember reading something about this a while back. I think it has to do with the way the iPad's Safari engine renders the pictures and how they get stored in the cache. Also, I think the iPad's limited RAM can't store too many large photos.
Just a suggestion, maybe you could create a dedicated iOS style to get rid of extraneous resources. Then write a Perl/CGI script to find the 40th or so picture (or however photos add up to 2.5MB), truncate it, and add a next link. Would it be difficult? Maybe. At least this way, users would only lose one or two photos (hopefully zero) instead of large amounts. Hope that helped you in any way/shape or form.