Child nodes are by default not added to the PrepareForReplicationNodes array in order to prevent unnecessary calls to PrepareForReplication. However, this difference in behavior is not very apparent when using root vs child nodes. If child nodes should not call PrepareForReplication, this difference should at least be made more clear.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-141192 in the post.