When entering many items, it's a very useful feature that a new line is automatically opened so you don't have to click "+ add item" (or just "+" in Kanban view) each time.
However, when you're just adding one item (which is often the case), opening of the item in order to enter information and/or child items would be more helpful.
Since there are two ways to save a newly added item – the space bar and the check mark button – my suggestion is to give each a different function, providing users more choice.
-> the space bar automatically triggering the new "add item" (so you don't have to go back and forth between keyboard and cursor)
-> the check mark button opening the newly created item (like when clicking the item, which you'd otherwise do manually)
