New roof: Should nails show through underside of decking in attic?

I had a licensed roofer put a new roof on my 15-year old, 2,000-square foot house in Florida (3-tab, 30-year architectural shingles). From the outside, looks like he did a nice job, but if you go into the attic, the tips of many of the nails drove all the way through the plywood decking... you can see maybe 1/4-inch to 1/2-inch of most the nail ends sticking through underside of the plywood. If you stand up in certain places in attic, you could get impailed by these exposed nail tips. Is this a normal or acceptable way to put on a roof, and/or what is the norm?