I did the same thing pulling the wheel off the body.
There is a post from DD4H about not making the axle holes too tight.
I learned my lesson from this break. The nail was simply in too tightly.
I never broke any running them............however........I've had about 4 break in shipping over the past year! One going to the race and 3 on the return..........The one going to the race sucked.........coming back home wasn't quite as bad, but still hurt as they were really good wheels!