Great advice Rarst! The output of $wpdb->queries was exactly what it should be:
"INSERT INTO `wp_featured_releases` (`fr_band`,`fr_album`,`fr_album_description`,`fr_image_id`,`fr_shop_url`,`fr_modified`) VALUES ('','','','504','','2011-01-14 10:49:58pm')"
504 is the correct id for the image, but the value in the table is still 127.
My latest thought is that my mysql skills have failed me. Images with an ID below 127 work fine, but anything above 127 is changed to 127. The column type that holds fr_image_id is tinyint(9), which should be able to hold any value up to 9999999999 right? If not, I think I just found my answer. I’ll try changing it and see.