As of recent, when I attempt to reorder folders in places by dragging them, the folder *above* the one being dragged gets reordered. E.g. if I have folders X, Y, Z ordered in Places like X Y Z and attempt to drag Z to the top, Y instead will be dragged to the top. Dolphin 18.04.2
I can also confirm this behavior with Dolphin 18.04.2. It might be related to D8855 as the placesitemmodeltest fails since this change was commited, but this is pure speculation.
*** This bug has been marked as a duplicate of bug 399430 ***