I just acquired a codex page in a guarded house in Venice. I went to Leonardo to have it decoded, and he said "Ah, this one is easy!". Next second I'm back on the street where a pickpocket is running away right in front of me. Funny thing was, once I killed the pickpocket I didn't get any money. I'm getting the feeling this was some kind of "new gadget" test or something that I didn't get.
I've been over every codex page in the database and I can't find one describing a piece of technology I don't already have. Also the Leonardo icon has disappeared from the map, and my inventory says I have 8 decoded and 0 encoded codex entries.
What the hell is going on?