Unless this has happened more than one tank I wouldn't be to worried about it. The pump probably shut off early but it was still high enough to show a full tank.
Green 2000 SVT #1166
mods-K&N and Custom heat shield, optimized y pipe, Magnaflow center resonator, DMDhttp://www.geocities.com/savinoss/Cars.html
-Wifes car 99 Mystique V6 5 spd