I was able to trace this to a bug and fixed it this afternoon. It will appear in the 2.4.6 release, due in a few weeks. Meanwhile, as John suggested, the workaround is to restart the app after making any change to a gallery setting (that is, a setting stored in gs_GallerySetting). This includes most pages in the Site admin area.
FYI, this bug also affects the "users to notify in case of error" setting.
Thanks for reporting this. Your detailed information was key in helping me reproduce it, which I was unable to do the first time it was reported.
Roger Martin
Creator and Lead Developer of Gallery Server Pro