Okay, problem solved.
32000 is a special group for 'unverified' users, this mean that they've provided a username and email address, but they've never came back. Only once they log in for the first time will they be moved to a 'real' group of your choosing.
I think that it might be worthwile making this explicit when you're looking at the profile of an 'unverified' user. It's tricky because you probably don't want to let people move users into this group, but when you move them into another group it's not obvious which group they're actually in (i.e. I thought these people were in group 5 from the web admin interface, but it turns out they weren't. From some other posts I found while searching this might already be the case. I think unverified users shouldn't be returned in the search for non-admins (maybe mods too) and that admins (maybe mods too) should be able to narrow the list to 'unverified' users and their title should be different from the default until such time as they verify.