Shaco not getting assist if ONLY the clone attacks target (without breaking)

Just played a game of shaco, and at one point I just popped ulti and made the clone attack the enemy champion and it died, but didnt get assist. I watched the replay and the clone indeed attack the target and even proc duskblade slowing the enemy. This surely cannot be a feature and must be a bug right? I mean j4 and put up a flag and get assist without actually attacking anyone.