I have it on good authority that if you think the standard early 747 was 'jumpy' at the back, you should try a ride in the NASA sShuttle transport. The wingtip vortices from the Shuttle lined up perfectly with the extra fin area added for directional stability; down the back you could see the whole fuselage twisting. 'Comments' were made, fatigue calculations done, and the answer was 'we're not doing a redesign now, put up with it'.