configuration of additional IPs v4 & v6


I wonder if something in Virtualmin changed with respect to the configuration of additional IPs.
For several years I had a working system by adding them in /etc/network/interfaces
putting in extra lines such as:

up ip addr add 144.xx.xx.216/32 dev $IFACE
down ip addr del 144.xx.xx.216/32 dev $IFACE
up ip addr add 144.xx.xx.217/32 dev $IFACE
down ip addr del 144.xx.xx.217/32 dev $IFACE

But now VirtualMin seems to overwrite this every time a new virtual host is added. (Ubuntu 14.04.1 and 12.04.2 on two different machines both have this problem with the current VirtualMin 4.11.GPL
So after every reboot I have to manually add them via the terminal with

ip addr add 144.xx.xx.216/32 dev eth0


I suspect one should add them via Networking -> Network Configuration -> Network Interfaces ?

Right now it has 1 entry with eth0 and the main IPv4 plus all the IPv6 (the latter don’t seem to work either).
Should additional IPv4 be added via the “Virtual Interfaces” link at the bottom of the existing eth0 setup? (see screenshot)

Is there a detailed documentation with some screenshots on how this should look? (I’m weary of making the system inaccessible if I misconfigure the network!)

My other problem is IPv6.
The IPv6 range is correctly defined in the VirtualMin server template and new sites get an allocated private IPv6, which then also shows up in /etc/network/interfaces and in the ifconfig output as lines of the form:

inet6 addr: 2a01:xxx:xxx:xxx::11/64 Scope:Global

but the virtual hosts with those IPs are still not accessible via their IPv6…

I would be most grateful for any pointers to solutions!