Hi,
OpenGL requires mipmap levels down to 1x1 (according to the red book), but DirectX can provide less levels, e.g. the smallest with 16x16. If I use such a mipmaped texture from d3d in opengl, this results in a white texture image. I've verified this with a GL-only program.
Never mind that, I just forgot to reduce the texture size for heigher levels. Now the mipmap example works fine. I don't know why my OpenGL test failed.