I think it's lag with the connections on your various clients. I get the same thing sometimes, and it is annoying, but I don't think there's anything you can do about it. I have a humorous vid I need to post that I took Friday of one of my toons 'swimming' in the air, while the others were mounted on their flyers. From her screen, it looked normal, but the other four toons showed her swimming in the air without a mount.