Unscheduled Server Maintenance - 01.06.2012

3 is correct.

1 is completely wrong.
Duping is always done by using the fact that the individual channel server processes keep information in internal memory for a while before forwarding it to the database server to be safely stored on disk. When the channel process crashes, the information in its memory is lost, resulting in a small rollback. This rollback can cause items to be duped.

I still don't get why equips don't have unique item IDs which are persistent. It shouldn't change the key when you put an item in storage, just copy it from one table to the other. And then when you go to insert it back in the first table, and a dupe exists, one of them would be automatically removed from the game. There's something weird going on if they can't even detect duplicate items... Use items are another matter, since all scrolls are alike (in order to stack) but most dupes do seem capable of duping equips.