Strange behaviour on compute shader

I've written a small compute shader that spit out positions for my geom shader. The threadGroup size is 4by4by4 and the group size just 1. So I get 4*4*4=64 positions where my geom shader have to generate a simple cube. But I get some strange behaviours... Even if I set all the buffer elements (my positions) to (1.0, 0.0, 0.0) I see more than one cube on the screen :( if I set the position directly in the geom(vert) shader to this value I have only my single cube, so it has to be something in the compute shader right?!

Is there someone having a similar problem or someone that can give me a hint of what causes this strange behaviour?