Updated both of my galleries (mine, Mysstie’s) to Zenphoto v1.5. Followed their upgrade instructions and backed up the themes and zp-core directories as well as the database before copying over the new files. I then used Windiff and code comparisons in PSPad to integrate any new changes in the default Garland theme into my custom Garland theme. The album.php, functions.php, image.php, news.php, pages.php, sidebar.php, themeoptions.php, and zen.css files were the only modified ones in this version from the previous. So far everything seems to work fine.
One of the main differences I discovered is how the thumbnail filenames are being generated. Before they had the format: filename_150_cw150_ch150_thumb.jpg and now: filename_150_w150_h150_thumb.jpg (even though the are still being cropped). So, I had to make sure all the new thumbnails got generated are were present in the /cache/ directory. I then had to change the random image code on my main website, the blog here, and Mysstie’s main site to use the new file format.