After further investigation... it doesn't seem to be exactly what i thought it was. It seems to be that when dragging around the lowest icon in the selection everything else keeps getting a bigger gap between the dragged icon and itself and that's why I thought the top icon remained in place when dragging the bottom icon to a lower position... it just happened to gain a gap that put it in it's previous position
After further investigation... it doesn't seem to be exactly what i thought it was. It seems to be that when dragging around the lowest icon in the selection everything else keeps getting a bigger gap between the dragged icon and itself and that's why I thought the top icon remained in place when dragging the bottom icon to a lower position... it just happened to gain a gap that put it in it's previous position