No, it works as designed. Changes you do through uci set etc. are staged in a temporary changes directory and reflected in the output of uci get, uci show etc.
A uci commit merges these temporary staged changes back into the persistent configuration files in /etc/config/. In practice this means that you can apply config changes without having to actually modify the /etc/config/ files on flash. This is especially useful for scripted actions, e.g. button press handlers or cron jobs where committing and altering config files all the time may wear out the flash.
After a reboot, all uncommitted configuration changes are gone.