I have two CM servers 5.1 (Pub & Sub) with two sites each server in a site (clustering over the WAN); and I have two CM groups one for each site (CM_GRP_site1 Pub then Sub) and (CM_GRP_site2 Sub then Pub)
Today with no reason the numbers (DNs) at site 2 changed (a phone that was registered with 8000 now have 8004) and this happens to all the site phones just it has random strange numbers.
I changed the CM_GRP_site to to let he phones register with the publisher it works fine and have thier correct DNs again. When I change it back the DNs changes again!!