ok I'll be the one to attempt a reply. I won't get into any discussions other than this reply so no mud slinging please.
Inflight and gate agents will often move our revenue passengers into the main J cabin to ensure that you the revenue passenger gets the quality service, meal and attention that is served in executive class. Many times these days inflight are not staffed for service to mini j so those seated there will have to wait longer and possibly not get the attention and service that is due. As for staff sitting in mini J, it is in many of the inflight's contract that under certain conditions they are entitled and will get J. So to ensure you, our revenue passengers receive the executive class service you will be seated in the full j cabin, staff will be in mini J.
Hope this clears up some of the questions. All in all it is done to ensure you are not short changed on the service.
Happy travels !