We are using a Kanban board with stories and sub-tasks. There are stories that are active on the board with sub-tasks that are in the backlog. The board filter is setup to use Rank.
I can move stories up and down in the backlog. I can move sub-tasks up and down within the group of sub-tasks. However I cannot move a sub-task from an active story on the board up to the top of the backlog.