C# - Why Does ReSharper Need To Scan All Files When Converting A Property To An Auto Property

Is there any difference between accessing a property that has a backing field

private int _id;
public int Id
{
get { return _id; }
set { _id = value; }
}

versus an auto-property?

public int Id { get; set; }

The reason I'm asking is that when letting ReSharper convert a property into an auto property it seems to scan my entire solution, or at least all aspx-files.

I can't see any reason why there should be any difference between the two from outside the class. Is there?