I did an experiment where I had a starship constructor on planet A rallying ships to my Ark. The Ark was on planet B. The Ark was moving to planet C, but still on planet B. The ships rallying to the Ark would get to the Ark, then not inherit the Ark's move command and just sit on planet B once they got to the Ark and stopped rallying.
I would like to propose the following. If the target of a rally is moving, and it is moving to another planet, anything rallying to that target should inherit the move commands of the target upon reaching the target.