glutBitmapCharacter does not work alone

[ISA]

The following little program illustrates the problem:

#include <GL/glut.h>

void draw() {
  glClearColor(0, 0, 0, 1);
  glClear(GL_COLOR_BUFFER_BIT);

  // Every matrix is identitiy at this point...

  glColor3f(1, 1, 1);
  glRasterPos2f(0, 0.1);
  glutBitmapCharacter(GLUT_BITMAP_8_BY_13, '1');

/* glBegin(GL_LINES);
   glVertex2f(0, 0);
   glVertex2f(1, 0);
  glEnd();*/

  glFlush();
}

int main(int args, char** argv) {
  glutInit(&args, argv);

  glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);

  glutCreateWindow("Main Win");

  glutDisplayFunc(&draw);

  glutMainLoop();

  return 0;
}

Compiled with:
gcc demo.c -o demo -lGL -lGLU -lglut

If executed it should show "1" but it does not. Only if uncommenting the drawing instructions for the following line it works. Generally, the function glutbitmapoCharacter seems only to work if something is drawn after calling the character draw function. glutStrokeCharacter seems to be affected by the same type of problem, however I did not check that as thouroughly.