Code Not Working Problem

Hello everyone, I'm having a hard time with some simple code.  When I click a run code button I get two lines of Hello World tacked onto a textbox instead of one.  I step through the code and see that the output function returns to the caller and gets called again for no apparent reason.  I just installed Web Developer 2012 Express yesterday and am just messing around with it to get familiar with it.  So after today's problems I installed Update 3 and it's still not working properly.  Is the code faulty?  Anyone have any advice to get this to work?  I did this in C# and VB.  In C# it works fine.  The problem is only with the VB version.  Here's the VB Code:
Partial Class _Default Inherits System.Web.UI.Page Protected Sub btnRun_Click(sender As Object, e As EventArgs) Handles btnRun.Click output("Hello World") End Sub Protected Sub output(value As Stri ...