It was in fact that line you identified in my global stanza that was causing my problem. I switched the setting to “security = user” and samba is back to giving me no problems. The line must have been changed somewhere in the transition.
The users, as you have probably guessed by the fact that my problem was solved, are in fact fullly privileged linux users. I did double check to re-add the users as root using smbpasswd -a [user], and ran the pdbedit -L -W again, and the output was quite the same. There must be some slight difference in the versions of samba run by SUSE or Ubuntu compared to Arch (one can only assume).
Anyhow, thank you for once again helping me solve my samba problems. After every hitch I come away with a slightly better understanding of the protocol. This topic is solved!