Anyone worked with gl2ps before?

I’m writing a small program that I’d like to render to an eps file so that I can use the images in latex . However when I render the eps file using the gl2ps library, one of the lines is not drawn. To see what I mean look at the following pictures:
the image I save as viewed from GSview:

and the bitmap image I save:

What troubles me is if for example I rotate the image, gl2ps saves the image just fine. Is there something I miss with gl2ps?
Here is the code I use to save the eps file:

void writefile(int format, int sort, int options, int nbcol,
               char *filename, char *extension)
  FILE *fp;
  char file[256];
  int state = GL2PS_OVERFLOW, buffsize = 0;
  GLint viewport[4];

  strcpy(file, filename);
  strcat(file, ".");
  strcat(file, extension);

  viewport[0] = 0;
  viewport[1] = 0;
  viewport[2] = glutGet(GLUT_WINDOW_WIDTH); //window_w;
  viewport[3] = glutGet(GLUT_WINDOW_HEIGHT); //window_h;
  fp = fopen(file, "wb");

    printf("Unable to open file %s for writing
", file);

  printf("Saving image to file %s... ", file);

  while(state == GL2PS_OVERFLOW){
    buffsize += 1024*1024;
    gl2psBeginPage(file, "test", viewport, format, sort, options,
                   GL_RGBA, 0, NULL, nbcol, nbcol, nbcol, 
                   buffsize, fp, file);
    state = gl2psEndPage();



Thanks for your time!