Everything is just fine now. Of course it was totally my fault, how could I dare to blame IC.
And I thought it would not work correctly wiring MV to a HVtf because the wiki said it only excepts 512 or 2048 EU as input. thats why there are MVtf directly before the HVtf at all. It would have been much more efficent to set them directly to the reactors ( or power source ) but i would not have 512 EU after a few blocks...