However, if you connect the second NIC to a working network, or set it to disabled, the power up sequence will be fine.
This is a Ubuntu feature I guess. Probably just a coincidence it shows up in U7 and not before. Did you update your Ubuntu packages?
So the solution for now is to disable any unused network ports if using DHCP. Multi-NIC computers are still good though, in the future I'll add LACP (Bonding) support so you can aggregate your network ports to the switch. In your case if you have two NIC, you will double the bandwidth from 1 Gbps to 2 Gbps.