Duplicating a possessable object binding in Sequencer causes a new sub track added to the existing possessable with a missing binding. It's unclear what the behavior should be here, as duplicating a possessable would also mean duplicating the object in the level.
A new subtrack is added to the existing possessable with a missing object binding. It's expected that a new object binding would be created as a new track, or that nothing would happen at all.
NOTE: In 4.22 the new object binding is still missing, but created as a new track, not as a subtract to the original object binding.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-86072 in the post.