Flex-end breaks dragging to parent element #1942

Reproduction

https://codepen.io/jjeff/pen/PozoJVQ

Scenario

SortableJS's normal behavior allows user to drag anywhere onto a Sortable list (including onto the draggable child elements) to add an element to it. However, with justify-content: flex-end; enabled on the parent Sortable element, you can no longer drag into the parent element. Dragging onto the child elements still works, but not onto the Sortable-enabled element itself.

See attached GIF and code at https://codepen.io/jjeff/pen/PozoJVQ. I can reproduce at Codesandbox if needed.

Steps to Reproduce

Summary of steps if applicable.

1. Add the following CSS targeting a series of lists in the same group:

  display: flex;
  justify-content: flex-end;

Describe the bug

Draggable child elements cannot be dragged to the parent Sortable element itself. Note that other justify-content values such as start, center, and space-around work fine.

Expected behavior

Dragging to parent should add dragged item as a child - preferably on the same end of the child list as the item was dragged.

Version

Additional Context