Does Jake not mean that the spacer can only accomodate a maximum hub depth of 10mm before it bottoms out, with the hub on this car being 11mm it would mean that the spacer wouldn't fit flush against the bell of the brake disc.
There would be a 1mm gap with the wheel bolts tightened which would result in the spacer being highly stressed and finally it broke to make the wheel loosen off by 1mm.
The spacers with the integrated hub centric ring also appear to be be very poorly designed with there being very little metal between the bore and the centric ring.
I think Chris is pointing to the fact that the hub centic rings quite often don't fit correctly, get lost and can be of a poor quality material.