I've got seven accounts online right now -- bonjour, zephyr, .mac, livejournal, yahoo, and a couple random jabber accounts. It's a private network, so no one else is on bonjour. My contact list includes a bunch of people with multiple accounts. When I can, I list all the accounts in Address Book and have Adium combine them; Address Book doesn't support Zephyr, so those I combine with the meta contacts directly in Adium. (Zephyr is also different from the others in storing the "contact" info locally and not on the server, and presence information is not acquired as part of sign-on, but requested from the server periodically, if those matter.)
Recently I was experimenting with a 1.3-debug build from Evan and 1.2.4b2. I just updated to 1.2.4b3, and brought all accounts online (using an "old-style SSL" workaround for the bug I was reporting before). I notice now that my Zephyr contacts are no longer combined with the non-Zephyr meta contacts for the same people. If I switch back to 1.3-debug, they're combined; back to 1.2.4b3 again, and they're separated. It looks like I can combine them again under 1.2.4b3 and it sticks.
I dug up a copy of 1.4.2b2, and it looks like the problem is there too; I was just focussed so much on the OpenFire issue (#9492) that I didn't really try out the Zephyr support. Looks like 1.4.2b1 has the problem too.
Console output includes a bunch of each of these:
2008-03-30 18:00:00.257 Adium[13629] Immediate reachability info for <NSCFType: 0x87075e0>
2008-03-30 18:00:00.257 Adium[13629] *** hostReachabilityChangedCallback got flags: -r-----
** (process:13629): CRITICAL **: purple_find_group: assertion `(name != NULL) && (*name != '\0')' failed
** (process:13629): CRITICAL **: purple_group_new: assertion `*name != '\0 failed
bunch more..
Mar 30 18:00:42 Kenneth-Raeburns-laptop /Applications/Adium.app/Contents/MacOS/Adium: CMSCreateDataProviderOrGetInfo : Invalid colorspace type
I can reproduce it in a new account by signing on with 1.2.3-debug to newly configured jabber and zephyr accounts (with a pre-existing jabber account with contacts), combining contacts under 1.2.3, quitting, starting 1.2.4 beta; the combined contacts are no longer combined.