If your job has multiple sync steps it's relativly easy for changelist reporting to display the built changelist twice.
Two possible improvements if this is under p4-plugin control:
(1) Are we able to aggregate changelists displayed in the 'Changes' panel of a completed job so each changelist only appears once?
(2) Are we able to report in the 'Changes' panel which checkout (for example syncID) caused each changelist to be displayed. This would help in troubleshooting/explaining duplicated changelists.