Hi Michael:
I have confirmed that images/move_subnet.png exists in the archive I released yesterday. If you can see the "delete subnet" button, you should see the "move subnet" button. Can you please try upgrading by this method to ensure files removed from the distribution are removed from your system and files added are added?
1. move your old collate:network folder to a new location, e.g. mv /var/www/html/ipam /var/www/html/ipam.bak
2. extract the new install to the old location, e.g., unzip Collate_Network_v1.7.2.zip && mv Collate_Network_v1.7.2 /var/www/html/ipam
3. copy the db_connect.php file containing your old settings to the new install path, e.g. cp /var/www/html/ipam.bak/includes/db_connect.php /var/www/html/ipam/includes/db_connect.php
If you still notice the problem after this, please let me know.
Thanks, -Jake