If Spark gets disconnected from Openfire for whatever reason (server reboot, network error, etc) and then automatically reconnects, all the entries in my contact list get duplicated. This is cumulative too, so if it disconnects/reconnects 3 times, I end up with 4 entries for every single person on my list.
If I exit Spark and reload it, the list returns to normal until the next disconnect/reconnect.
See screenshot below: