Rearrange by right-button drag not working across rows

I use double-height taskbar.  When one group spans the rows, I can't move the last item in a group (which is on the 2nd row) to the beginning of the group (which is on the 1st row) using right-button drag.  I can move the item to some *other* group in the top row, but not to the same group.

Dragging thumbnail previews works, but I would like to turn off thumbnails and just reposition taskbar items directly.