Sync AnimationMixer to objects added later

I’ve got an animation mixer that plays through an animation once and then clamps at the end. Now I want to add another object to the animation group, after the animation has completed. Is there a way I can get the mixer to “sync” the newly-added object so that it will be positioned according to the current state of the animation?

Actually, what’s strange is that if I add an object to the group after the animation has finished, even restarting the clip from the beginning doesn’t seem to affect the new object.