By default, subtickets are displayed 2 times.
One time in the grid and one time by clicking on the "+" button next to the parent ticket.
After click on the "+" button next to the parent ticket, the duplicate disappear and the subtickets still only viewable via click on the "+" button
From my point of view, it should be better to have the default view directly with the subtickets regrouped (for avoid to see too much informations on screen)
To add to this, it would be great if you could add a single update to the parent or close the parent and it would update the child or close the child tickets.