Can't drag the first subtask of a task to be a child of the next task on the planning board

In the list view of the planning board, with a set of tasks and subtasks in the following structure:

A
->A1
->A2
->A3
B
C

• If the user picks up A and drags it around, the items in the list move out of the way so that it can be dropped between them.
• If the user picks up A3 and drags it around, the items in the list stay still so that it can be dropped on top of them.
• However, if the user picks up A1 and drags it around, items move out of the way. This means that A1 cannot be dropped such that it becomes a child of B because B keeps moving out of the way.