Duplicate Groups and Calenders shown in System Preferences

Each record has it's own unique ID. Every time the client is disable / re-enabled iSync generated new IDs for each record. This causes the IDs on the server to no longer match those on the client (iSync), and hence two separate records are displayed. A long time ago I used the group name instead of the ID, however this caused problems when groups on the client were renamed, and having multiple groups with the same name also was not supported. To resolve this issue and combine the records, you select both rows and sync. During the sync similar records will be merged and combined into a single one.