Cisco Firewall :: ASA 5520 - Sub-interfaces With IPv6 Prefix

We have been testing out IPv6 configurations on a 5520 running 8.2(4).  We have assigned EUI-64 prefix addresses to sub-interfaces to allow clients to auto-configure there IPv6 IPs and it works correctly.   I used ASDM to do the original configuration and noticed that there were two different ways to do it, both of which seem to work.  I can add a prefix under the Interface IPv6 Addresses dialog box and check EUI64 or I can add it under the Interface IPv6 Prefixes.  But using the two methods yields two different interface configurations:
 
1.
interface GigabitEthernet0/1.40
vlan 40
nameif test

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