i had a similar problem in my old car. it would shut off completely after putting in less than 1 gal into a 13 gal tank.

i started inserting the pump nozzle into the filler tube varying lengths. sometimes i had to only put it half way in or it would stop, sometimes i could go 3/4 way, etc.

it has to do with the air pressure being relieved in the filler tube and the tank, which many people here have already mentioned.

i have a new 05 Prius (28 days old today) and have had no problems during my 2 fillups. it may be an anomaly with your car. either way, good luck!