I've just tried to compile a new project for the first time, and I find that at least one un-wanted class is being added.

Unfortunately, Code References is no help to you here. There is a reason that they call it Code References.

What you can do is use this code to search for a given string in the ClassLoc field of all your vcx's or scx'x. If you open one of the unwanted classes in the class designer, you should be able to see which class library it is in.

Local lnFiles, lcCurdir, lnCnt, lcFile
lcCurdir = Fullpath( Curdir() )
Cd ( << whatever subdirectory you want to search >> )
lnFiles = Adir( laFiles, '<<*.scx or *.vcx >>' )
For lnCnt = 1 To lnFiles
  lcFile = Forceext( laFiles[ lnCnt, 1], '<<*.scx or *.vcx >>' )
  Use (lcFile)
  Locate For Lower( Alltrim( '<< string that you are searching for >>' ) ) $ Lower( classloc )
  If Found()
    ? lcFile
  Endif
Next
Cd ( lcCurdir )