weird texture behaviour

using the code from nehe's lesson 10 i load the same texture in multiple ways and switch between modes with pressing "f".

glGenTextures(3, &texture[0]);
	 
    // mode 1
    glBindTexture(GL_TEXTURE_2D, texture[0]);   // 2d texture (x and y size)
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST); 
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST); 
    glTexImage2D(GL_TEXTURE_2D, 0, 3, image1->w, image1->h, 0, GL_RGB, GL_UNSIGNED_BYTE, image1->pixels);

    // mode 2
    glBindTexture(GL_TEXTURE_2D, texture[1]);   
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); 
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_LINEAR); 
    glTexImage2D(GL_TEXTURE_2D, 0, 3, image1->w, image1->h, 0, GL_RGB, GL_UNSIGNED_BYTE, image1->pixels);

    // mode 3
    glBindTexture(GL_TEXTURE_2D, texture[2]);   
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); 
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_LINEAR);
    gluBuild2DMipmaps(GL_TEXTURE_2D, 3, image1->w, image1->h, GL_RGB, GL_UNSIGNED_BYTE, image1->pixels);

it starts out with GL_NEAREST for MAG- and MIN-FILTER(mode 1). notice that mode 2 and mode 3 are the exact same. but when i press "f" once (going in mode 2 then) all textures become white. but if i press "f" a second time i'm in mode 3 (which should be the same as mode 2) everything looks fine again. why does that happen? also: my app runs faster in fullscreen. why?