system-config-users displays same user in multiple groups

Issue

system-config-users displays the same user for every group with the same GID as the user's primary GID.
We have multiple groups with the same GID to work around the 1024 character limit in NIS entries, i.e., there are too many users in the group to fit on one line.

For example, susie's primary group is GID 1000 which is split into multiple groups:
/etc/passwd

susie:x:888:1000:Susie Smith:/home/susie:/bin/bash

/etc/group

largegroup01:x:1000:user1,user2,user3,...
largegroup02:x:1000:user100,user101,user102,...
largegroup03:x:1000:user200,user202,user203,...

system-config-users shows susie as a member of largegroup01, largegroup02, and largegroup03:

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