Not quite sure I get you, as it would normally rotate - Are you saying it will only turn 6mm ? The two nuts and the spacer should all be tight.
The Mavic hubs have cartridge bearings (as you'll know) but you can adjust the 'pre-load' with the 'nuts' just like you can with a standard wheel. What you do need to make sure is the pre-load is ideally just tight enough to cause a little 'wobble' before you pop in in the drop outs. On tightening, you should feel no clunking when you grab the tyre.