In the spirit of GTD (tm), we've improved the ability to filter on your "Inbox" of untriaged tasks. A task that is a subtask of another in Agile Task Planner will automatically have the "@inherit-horizon" label applied. Now you can update your board to have an "Inbox" filter that shows you the tasks with no horizon, while eliminating the noise of subtasks. We also added the "[None]" and "[Inherit]" options to the Horizons drop-down menu.
More info: https://agile-innovations.atlassian.net/wiki/spaces/ATPD/pages/648577025/Board+Configuration