Mac OS X system user accounts

I seldom mess around in the Accounts Preference Pane but yesterday I had reason to do so, only to rediscover a long time problem I've had with this preference pane. For some reason an exception was thrown when the pane was activated, making it almost unusable. According to console.log the exception was raised because a nil string (or other) argument was passed to NSCFString's -replaceCharactersInRange:withString:. The whole thing was driving me mad.

I finally found out that a few system user accounts I've created didn't have a realname property. These system accounts also had uids starting at 1000 which apparently triggers the exception. I guess the Accounts Preference Pane interprets high uids to mean the users are a real users and so wants to find a realname property. I'm not sure where the limit is on system users versus real users, but 100 rings a bell. Oh well, the pane is working again even if the user list is populated with a few system users.