This is a bug that I have found twice in the last couple of days:

EnvDTE.CodeElement.GetStartPoint(vsCMPart.vsCMPartBody) returns wrong result for VB.NET classes using the Implements or Inherits clauses
http://www.mztools.com/articles/2009/MZ2009016.aspx

The bug was not present in VS.NET 2003, it appeared in VS 2005, it is in VS 2008 and also in VS 2010 Beta 1. You can vote to get it fixed here:

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=475961