While bringing up a BGP session for a client I kept trying to add our side of a /126. It kept reverting to the network address. The video shows what happens when I tried to add ::12/126 to the IPV6 addresses.
After some second-guessing and then some Facebook chatting I decided to do a terminal /ipv6 address print. Sure enough the proper IP shows up. Must be a GUI bug.
MTIN Family of Sites