Do you mean like this
http://www.gasgasrider.org/forum/showthread.php?t=2566 ?
I had the shop rebuild my rear wheel with the allballs kit, they must have thrown out the spacer, and just run the bearings, it probably lasted 200 odd km before the sprocket side spacer broke the center of the bearing and ceased onto the spacer. Made a rather strange noise after that....haha. I was lucky it lasted that long though, because it happened after a ride where there were sections that were tapped in 6th gear over sandy whoops, would not have been cool for them to fail then.
The shop replaced them at their cost, with the spacer
no problems since.