I can't reproduce the behavior with my current setup. Try enabling Log errors during checkout to watchdog
and Display debug information to administrators. at admin/store/settings/quotes/edit , and checking the logs for any error message. If you can, please send-me a dump of your uc_global_quote and uc_shipping_zones db tables it will also be really helpful. By the way I'll try to make a second look tomorrow
Did you manage to add more than one zone with the same country?
You can grab the latest version (with decimals) from that url: https://github.com/joanpc/uc_global_quote/tarball/master