I believe that starting with MDT 2004, AMBALLOON behavior was changed so that balloons did not move as an assembly was updated, only the leader stretches. I have had similar problems, especially in exploded isometric assemblies, with balloons not moving with the updated parts and creating a real mess in the drawing (See thread titled AMBALLOON Still Broke, about July of this year). I was told that this cannot be fixed in a service pack because its not considered a bug and would be a new feature. The earliest it will be considered to possibly offer the old functionality will be in a future release. Until then, I guess we gotta live with it.