Well, if your looking at the file in the location its downloading to, it will say how big the file will be when it has finished downloading, i cant tell you exactly why to be honest, but thats the way it is. It may have something to do with the fact that windows is just allotting the space the file is going to take up for it ahead of time.
Your other question is confusing though. You can see that it has downloaded 2mb, so thats how big it is at that point in time. Why does it matter what it says in the folder your downloading it to? You know its going to be 400mb when its done, you know that its currently 2mb. I might be misunderstanding something here, sorry ahead of time if so.
For the last part, same thing as above, windows is showing you how much space has been allotted for the file ahead of time.