When using drag-and-drop to reorder a category group in Categories, only the group heading is moved during preview, not the group's children. This is confusing as eventually, when dropping, the whole group is indeed moved with its children.

Note: this is only a visual bug on the preview. The final category group reorder works as expected.

I understand that having something too big on the preview could be annoying if the group is big. Some websites shrink/fold the children in the dragged preview in the form of a small rectangle with a number such as "(with 5 categories below)" to avoid this issue, while either a. completely removing, or b. greying out the children about to be moved to show that they will be moved, while letting user still see where they were before the move.