I'm obviously not spending enough time with coding OpenGL these days. The reason that the GLU tessellation callbacks were messed up was that I was mis-reading the spec and trying to convert pointers to Vertex objects into double arrays. I went through altering the OpenGLContext code to work with vertex pointers before I realised "wait a minute, this worked fine with PyOpenGL, what am I missing" and actually read the spec for the functions... which exactly matched what the OpenGLContext code was doing, of course.

Anyway, the fixes are now in CVS.