What is the behavior change between 6.1 and 6.3 with respect to IPmobility ?
IPMobility has gone through major changes from 6.1 to 6.3. L3 mobility support for ipv6 and dual stack clients came as part of 6.3. During 6.3 mobility architecture has gone through major changes. To be more specific looking at the changes that happened for home-agent discovery; In 6.1 home-agent discovery was done using ip address and mobility snooped on DHCP packets from client to know which ip address they got assigned to.
This has changed in 6.3 (because single client can have multiple ipv6 addresses). So, from 6.3 onwards home-agent discovery is done using client mac address. Moreover, with 6.3 home-agent discovery happens when client associates (even before dhcp starts, in case of dynamic ip clients).
As dhcp is treated as any other data traffic from client the dhcp finite state machine is removed from mobile ip. Similarly mobile ip finite state machine has gone through major changes to do home-agent discovery at the client association.