When traversing a QTreeView using the arrow keys, items behave as if they could be expanded even though they do not have any children.
I.e. hitting the right arrow key will expand the tree, hitting right again would take you one level down. If you hit the right arrow key when the item does not have any children, you would need to hit the left arrow key twice to go back up. One to seemingly collapse the tree, and one to move up one level.

This can be reproduced with the simpletreemodel example.