Freezes for 10 seconds in IE only when pressing F5

Hi,
I have a very simple app I just started with a ComboBox on a Web Form in C# 4.5.1 in Visual Studio Community 2013.  The ComboBox is filled in the Page_Load with a if(!Page.IsPostBack) and when I debug it passes all right very rapidly on the code but when I'm presented with the interface, I can't click on the ComboBox for about 10 seconds.  This is very long for just 4 rows coming from the DataTable.
Now here is the fun part if I I Start the app using Google Chrome, it's instantaneous.  I can click immediately on the ComboBox and I see the 4 element there.  Why IE has this behaviour ? while running my ASP.NET Web Form ?