When flying in jet or any other vehicle that is moving, when you press M you can hear your vehicle move away as the camera stay in place which will cause loading time after closing the map when the vehicle moved to far away.
And that loading time after you close map is caused by detached camera after pressing M. (at least i think so)
Im sure you guys also experienced it while being in helicopter and after pressing M you heard as the sound fade away and after closing map there was short loading time.