I think there is some strange behaviour when creating/modifying additional Addresses...
first you need at least one additional addresses
then go in Network/Additional Addresses and click on new address
you can start setting the address...
do not click on save... just click on edit for another address on the right... this fill automatically the new address field... so we can expect this can be used as a template for the new IP as the Title keep saying "New Additional Address" !!!! which is not the case as if u click save it is for the other ip you clicked on edit...
so this is quite anoying... you should either use it as a template and if clicking on save without changing ip it should say ip already in use... or you have to change the box title saying it's modifying or have a warning or something...
thx