[color:"orange"]Why is it a problem to move the hero and DK potraits over?[/color]
When dealing with the hero, for example, it is better to always click on (or drag-and-drop to) the top right corner, than to usually do so, but sometimes it is over one slot, or two slots, or whatever. Especially in the heat of battle (when most likely to use summoning dolls), you do not want to be moving interface elements around.
[color:"orange"]Your argument about summoning dolls makes it worse - it will be harder to remember which summon is which when there's six chars to control.[/color]
How does the display order help tell the difference between summoning dolls? Presumably by the time you have found 4 summoning dolls, you should be familiar with their portraits and body types (I doubt they would all be identical). You would summon them in a specific order, when using more than one, and should just know that the first one summoned becomes character 3, etc. Even if you had to count the portraits every time you wanted to use a hotkey to select a character, counting to 6 right to left isn't significantly harder than doing so left to right.
[color:"orange"]Show the icons in the correct order and it's obvious at a glance. BD will attract a lot of criticism if it can't get simple and obvious interface elements right.[/color]
So left to right is the one-and-only 'correct' order?
I am used to changing reference systems to whatever is appropriate to the situation.