World in flames - Units Random Selection Problem

Hi, I am now trying to setup the global war scenario. I realize there is a random selection function by right clicking on a stack but it seems the selected units are not random. They are still following the original order of the stack. Could someone help on this? Thanks.

You just drag one unit out by holding down a left click and dragging from on top of the stack. It is randomly chosen and so will not always be the one you see on top.

Also you can right click and choose a quantity of units. They will be randomly chosen from among the stack contents when you drag them out.