Yep, this happened to me and a passenger yesterday. The grey box landed on me and I couldn't move or control my boat. Only a log-out cleared it but the box was still on the boat with the passenger. The second time it hit my passenger and that was on a different boat. It only occurs on sim crossings. It also seems to break the copy of the boat, as I deleted both versions and then re-rezzed them with the box still attached to the object.