If you adopted VB.Net when it first appeared in Visual Studio 2002, you probably have some projects and/or forms here and there that followed you towards the years.
If you remember when Visual Studio 2005 was released, the format of the files changed a bit. Instead of adding a “Windows Form Designer Generated Code” region at the top of your code, Microsoft decided to isolate this code into a new .designer.vb file. When you upgraded projects from Visual Studio 2002/2003 to Visual Studio 2005 or 2008, this “untouchable” region remained right there.