After some thought there is nothing wrong with your car than probably a defective glow relay. When you first turn the key even though the glow light does not activate the plugs are on.
The reason the voltage drop is a little greater is the colder the plug the more initial current surge is occuring. When you turn the key the second time the light comes on and the current draw is a little lower because the plugs have warmed a little from the first partial glow cycle.
You had me going for a minute or two with your description. Although logic said other than a shorted alternator this could not happen. The alternator would not function normally a minute later after starting. . All other circuits are moderatly fused and I kind of eliminated the starter as well.
Had there been something funny in the key switch area you would have smelt the wires burning at those large current draw levels. I have seen glow relays act exactly as yours is right now on older 123s. It is almost as if the glow plug bulb latching circuit will not activate with the first key try. Yet it does the second try. Some take three or four tries.
I would grab another relay from an auto salvage place or borrow one for a test to verify it first as they are not too cheap new. This should stop all your concern at present as well. If you are still uncertain just monitor the plug voltage when you turn the key the first time. I believe it will be there. Where else really could a current of this magnitude be going with out any other symptoms? It's just elementary Watson.
If it is not as I sugest just do not pay my bill.
Yet still post the answer so other people can draw and quarter me if wrong.
Too cool to be fooling around out there anyways in most north american locations right now.
