Writing with glBitmap directly to the front buffer when using double-buffering seems to have no effect. Other routines such as GL_QUADS seem to work.  

Configuration: 
  * ATI radeon X1400 (R520), but the same behavior is observed with LIBGL_ALWAYS_INDIRECT=1
  * Fedora 12-packaged mesa-libGL-7.6-0.13.

I am using the front buffer directly for a mouse tracker and don't want to have to fully redraw to avoid excessive slowness when run over remote X. 

Code example: 

  glDrawBuffer(GL_FRONT);
 
  /* Erase background first */
  glColor3f(0.0,0.0,0.0);
  glBegin(GL_QUADS);
  glVertex2i(poslinex,posliney);
  glVertex2i(poslinex+poslinewidth,posliney);
  glVertex2i(poslinex+poslinewidth,posliney+poslineheight);
  glVertex2i(poslinex,posliney+poslineheight);
  glEnd();

  /* draw a character */
  glColor3f(1.0,1.0,1.0);
  glRasterPos2i(poslinex,posliney+poslineheight);
  glutBitmapCharacter(TextFont,'f'); /* thin wrapper over glBitmap() */

  glFlush();

  glDrawBuffer(GL_BACK);

Expected result: draw an 'f' over a black rectangle
Actual result: Black rectangle but no 'f'. 

Removing the glDrawBuffer() calls and adding
glutSwapBuffers() at the end solves the problem and the expected
result is achieved.