I'm attempting to use the GLU nurbs functions to display trimmed nurbs, but have run into some problems.  The first few surfaces I draw display just fine, but eventually, a GL_STACK_OVERFLOW exception is raised when gluEndSurface is called.  It doesn't seem to depend on the surface itself.  I get the error whether I display a short list of surfaces many times (e.g. rotating, etc) or a long list once.  Eventually the stack overflow occurs.  I think the problem is associated with trimming, because if I draw the surfaces without trimming, the error does not occur.    I'm running Ubuntu Linux 9.04 (Mesa 7.6 libGLU), Nvidia drivers/core OpenGL, and pyopengl 3.0.0.  I've duplicated the problem on an RHEL 5.4 installation.