Why do the EnvDTE.dll and dte80a.olb files appear in Detected Dependencies in my VS2008 web deployment project?

I have a VS2008 web project which was originally migrated from VS2003.

In my solution, I have a web deployment project which uses the Primary Output and Content Files (+ some support files) from this web project to build an msi package.

The problem is that under "Detected Dependencies", I see the files EnvDTE.dll and dte80a.olb. Furthermore, the EnvDTE.dll file is actually picked up from

C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\PublicAssemblies\EnvDTE.dll

which is the VS2005 installation folder - not the VS2008 one.

The original VS2003 solution, of course, does not pick up such a VS2005 file, but it does not pick up anything similar either.

None of the (sub)projects in my solution make use of EnvDTE.

Can anyone explain to me under which conditions a VS2008 web deployment project would pick up these files in Detected Dependencies (given that there are no references to EnvDTE anywhere in the solution)?